Revert RecursiveASTVisitor fixes.

This reverts commit 8bf4c40af813e73de77739b33b8808f6bd13497b.
This reverts commit 7b0be962d681c408c8ecf7180c6ad8f9fbcdaf2d.
This reverts commit 94454442c3c15a67ae70ef3a73616632968973fc.

Some compilers on some buildbots didn't accept the specialization of
is_same_method_impl in a non-namespace scope.

GitOrigin-RevId: 19eaff650c9c091e844f0a342540f1d10573772c
3 files changed