[DOCS] Remove outdated paragraph (#1581)

There is no necessity anymore for user functions to be prepended with `user_` anymore, so that confusing and vague sentence can be removed.

Author: FlyKasual

Documentation/Functions/Parsefunc.rst

@@ -167,9 +167,6 @@ userFunc
     Similar to, for example, :ref:`stdwrap-postUserFunc` in :ref:`stdWrap`,
     or :ref:`typolink.userFunc <typolink-userFunc>`.
 
-    Remember the function name must possibly be prepended :php:`user_`.
-
-
 ..  _parsefunc-nonTypoTagStdWrap:
 
 nonTypoTagStdWrap