Revert counted_by attribute feature (#75857)

There are many issues that popped up with the counted_by feature. The
patch #73730 has grown too large and approval is blocking Linux testing.

Includes reverts of:
commit 769bc11f ("[Clang] Implement the 'counted_by' attribute
(#68750)")
commit bc09ec69 ("[CodeGen] Revamp counted_by calculations
(#70606)")
commit 1a09cfb2 ("[Clang] counted_by attr can apply only to C99
flexible array members (#72347)")
commit a76adfb9 ("[NFC][Clang] Refactor code to calculate flexible
array member size (#72790)")
commit d8447c78 ("[Clang] Correct handling of negative and
out-of-bounds indices (#71877)")
Partial commit b31cd07d ("[Clang] Regenerate test checks (NFC)")

Closes #73168
Closes #75173