[AIX][libc++] Enable clang_modules_include.gen.py tests (#90971)

Enable these tests on AIX since they're passing.

Author: jakeegan

libcxx/test/libcxx/clang_modules_include.gen.py

@@ -31,9 +31,6 @@
 // UNSUPPORTED: windows
 // UNSUPPORTED: buildhost=windows
 
-// The AIX headers don't appear to be compatible with modules
-// UNSUPPORTED: LIBCXX-AIX-FIXME
-
 // The Android headers don't appear to be compatible with modules yet
 // UNSUPPORTED: LIBCXX-ANDROID-FIXME
 
@@ -61,9 +58,6 @@
 // UNSUPPORTED: windows
 // UNSUPPORTED: buildhost=windows
 
-// The AIX headers don't appear to be compatible with modules
-// UNSUPPORTED: LIBCXX-AIX-FIXME
-
 // The Android headers don't appear to be compatible with modules yet
 // UNSUPPORTED: LIBCXX-ANDROID-FIXME