logictest: remove cockroach-go-testserver-25.3 configuration

Part of the quarterly M.4 "Bump MinSupported" task as outlined in
`pkg/clusterversion/README.md`.

After bumping MinSupported from v25.3 to v25.4, the cockroach-go-testserver-25.3
configuration and related mixed-version tests are no longer needed:
- Clusters can no longer start below v25.4 (MinSupported)
- Mixed-version tests that check for v25.4 features are now obsolete since
  all clusters start at v25.4 or higher

This commit:
- Removes the cockroach-go-testserver-25.3 configuration from logictestbase.go
- Deletes the cockroach-go-testserver-25.3 test directory
- Deletes obsolete mixed-version test files:
  - mixed_version_ltree: Tested that LTREE is only available after upgrading to 25.4
  - mixed_version_partial_stats: Tested partial stats availability after upgrade to 25.4
- Regenerates Bazel BUILD files via `./dev gen bazel`

Following the pattern from reference PR #157767, which removed
cockroach-go-testserver-25.2 when MinSupported was bumped from v25.2 to v25.3.

Release note: None

Author: celiala

pkg/BUILD.bazel

@@ -518,7 +518,6 @@ ALL_TESTS = [
     "//pkg/sql/logictest/logictestbase:logictestbase_test",
     "//pkg/sql/logictest/tests/5node-disk:5node-disk_test",
     "//pkg/sql/logictest/tests/5node:5node_test",
-    "//pkg/sql/logictest/tests/cockroach-go-testserver-25.3:cockroach-go-testserver-25_3_test",
     "//pkg/sql/logictest/tests/cockroach-go-testserver-25.4:cockroach-go-testserver-25_4_test",
     "//pkg/sql/logictest/tests/fakedist-disk:fakedist-disk_test",
     "//pkg/sql/logictest/tests/fakedist-vec-off:fakedist-vec-off_test",
@@ -2091,7 +2090,6 @@ GO_TARGETS = [
     "//pkg/sql/logictest/logictestbase:logictestbase_test",
     "//pkg/sql/logictest/tests/5node-disk:5node-disk_test",
     "//pkg/sql/logictest/tests/5node:5node_test",
-    "//pkg/sql/logictest/tests/cockroach-go-testserver-25.3:cockroach-go-testserver-25_3_test",
     "//pkg/sql/logictest/tests/cockroach-go-testserver-25.4:cockroach-go-testserver-25_4_test",
     "//pkg/sql/logictest/tests/fakedist-disk:fakedist-disk_test",
     "//pkg/sql/logictest/tests/fakedist-vec-off:fakedist-vec-off_test",

pkg/sql/logictest/logictestbase/logictestbase.go

@@ -508,14 +508,6 @@ var LogicTestConfigs = []TestClusterConfig{
 		DisableUpgrade:              true,
 		DeclarativeCorpusCollection: true,
 	},
-	{
-		// This config runs a cluster with 3 nodes, with a separate process per
-		// node. The nodes initially start on v25.3.
-		Name:                     "cockroach-go-testserver-25.3",
-		UseCockroachGoTestserver: true,
-		BootstrapVersion:         clusterversion.V25_3,
-		NumNodes:                 3,
-	},
 	{
 		Name:                "local-leased-descriptors",
 		NumNodes:            1,
@@ -656,7 +648,6 @@ var DefaultConfigSets = map[string]ConfigSet{
 
 	// Special alias for all testserver configs (for mixed-version testing).
 	"cockroach-go-testserver-configs": makeConfigSet(
-		"cockroach-go-testserver-25.3",
 		"cockroach-go-testserver-25.4",
 	),