[flang] Fix issue flang-compiler/f18#515

Do not emit "is not a branch target" warning for old action-stmt just
because these action-stmt are depreciated. The depreciated aspect of
these features is already handled via -Mstandard.

Original-commit: flang-compiler/f18@f7d124d8cd3d97ee81208121a336f14fef9595ac
Reviewed-on: https://github.com/flang-compiler/f18/pull/593