Python: Change perf fix PoorMansFunctionResolution

Thanks @yoff, this leaves us with the following evaluation, which looks
very close to the one in the other fix (but with cleaner implementation)
-- both at 688k max tuples (although numbers are not exactly the same).

```
[2021-11-24 13:48:40] (14s) Tuple counts for PoorMansFunctionResolution::getSimpleMethodReferenceWithinClass#ff/2@e5f05asv after 74ms:
                      47493  ~3%     {3} r1 = JOIN Class::Class::getAMethod_dispred#ff WITH py_Classes ON FIRST 1 OUTPUT Lhs.1, 0, Lhs.0
                      47335  ~0%     {2} r2 = JOIN r1 WITH AstGenerated::Function_::getArg_dispred#fff ON FIRST 2 OUTPUT Rhs.2, Lhs.2
                      46683  ~0%     {2} r3 = JOIN r2 WITH DataFlowPublic::ParameterNode::getParameter_dispred#fb_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1
                      259968 ~4%     {2} r4 = JOIN r3 WITH LocalSources::Cached::hasLocalSource#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1
                      161985 ~0%     {3} r5 = JOIN r4 WITH Attributes::AttrRef::accesses_dispred#bff_102#join_rhs ON FIRST 1 OUTPUT Rhs.1 'result', Lhs.1, Rhs.2
                      161985 ~2%     {3} r6 = JOIN r5 WITH Attributes::AttrRead#class#f ON FIRST 1 OUTPUT Lhs.2, Lhs.1, Lhs.0 'result'
                      688766 ~0%     {3} r7 = JOIN r6 WITH Function::Function::getName_dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Lhs.1, Rhs.1 'func', Lhs.2 'result'
                      20928  ~0%     {2} r8 = JOIN r7 WITH Class::Class::getAMethod_dispred#ff ON FIRST 2 OUTPUT Lhs.1 'func', Lhs.2 'result'
                                     return r8
```

Author: RasmusWL

python/ql/lib/semmle/python/frameworks/internal/PoorMansFunctionResolution.qll

@@ -62,49 +62,19 @@ private DataFlow::TypeTrackingNode poorMansFunctionTracker(DataFlow::TypeTracker
   exists(DataFlow::TypeTracker t2 | result = poorMansFunctionTracker(t2, func).track(t2, t))
 }
 
-/** Helper predicate to avoid bad join order. */
-pragma[noinline]
-private predicate getSimpleMethodReferenceWithinClass_helper(
-  Function func, Class cls, DataFlow::AttrRead read
-) {
-  DataFlow::parameterNode(func.getArg(0)).flowsTo(read.getObject()) and
-  cls.getAMethod() = func
-}
-
-/**
- * Helper predicate to avoid bad join order, which looked like:
- *
- * (8s) Tuple counts for PoorMansFunctionResolution::getSimpleMethodReferenceWithinClass#ff/2@cbddf257 after 8.6s:
- * 387565   ~0%     {3} r1 = JOIN Attributes::AttrRead#class#f WITH Attributes::AttrRef::accesses_dispred#bff ON FIRST 1 OUTPUT Rhs.2, Lhs.0 'result', Rhs.1
- * 6548632  ~0%     {3} r2 = JOIN r1 WITH Function::Function::getName_dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1 'func', Lhs.1 'result', Lhs.2
- * 5640480  ~0%     {4} r3 = JOIN r2 WITH Class::Class::getAMethod_dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'result', Lhs.2, Lhs.0 'func'
- * 55660458 ~0%     {5} r4 = JOIN r3 WITH Class::Class::getAMethod_dispred#ff ON FIRST 1 OUTPUT Rhs.1, 0, Lhs.1 'result', Lhs.2, Lhs.3 'func'
- * 55621412 ~0%     {4} r5 = JOIN r4 WITH AstGenerated::Function_::getArg_dispred#fff ON FIRST 2 OUTPUT Rhs.2, Lhs.2 'result', Lhs.3, Lhs.4 'func'
- * 54467144 ~0%     {4} r6 = JOIN r5 WITH DataFlowPublic::ParameterNode::getParameter_dispred#fb_10#join_rhs ON FIRST 1 OUTPUT Lhs.2, Rhs.1, Lhs.1 'result', Lhs.3 'func'
- * 20928    ~0%     {2} r7 = JOIN r6 WITH LocalSources::Cached::hasLocalSource#ff ON FIRST 2 OUTPUT Lhs.3 'func', Lhs.2 'result'
- *                                        return r7
- */
-pragma[noinline]
-private predicate getSimpleMethodReferenceWithinClass_helper2(
-  Function func, Class cls, DataFlow::AttrRead read, Function readFunction
-) {
-  getSimpleMethodReferenceWithinClass_helper(pragma[only_bind_into](func),
-    pragma[only_bind_into](cls), pragma[only_bind_into](read)) and
-  read.getAttributeName() = readFunction.getName()
-}
-
 /**
  * Gets a reference to `func`. `func` must be defined inside a class, and the reference
  * will be inside a different method of the same class.
  */
 private DataFlow::Node getSimpleMethodReferenceWithinClass(Function func) {
   // TODO: Should take MRO into account
-  exists(Class cls, Function otherFunc |
-    cls.getAMethod() = func and
-    cls.getAMethod() = otherFunc
+  exists(Class cls, Function otherFunc, DataFlow::Node selfRefOtherFunc |
+    pragma[only_bind_into](cls).getAMethod() = func and
+    pragma[only_bind_into](cls).getAMethod() = otherFunc
   |
-    getSimpleMethodReferenceWithinClass_helper2(pragma[only_bind_into](otherFunc),
-      pragma[only_bind_into](cls), pragma[only_bind_into](result), pragma[only_bind_into](func))
+    selfRefOtherFunc.getALocalSource().(DataFlow::ParameterNode).getParameter() =
+      otherFunc.getArg(0) and
+    result.(DataFlow::AttrRead).accesses(selfRefOtherFunc, func.getName())
   )
 }