[libc++] Remove the legacy debug mode.

See https://discourse.llvm.org/t/rfc-removing-the-legacy-debug-mode-from-libc/71026

Reviewed By: #libc, Mordante, ldionne

Differential Revision: https://reviews.llvm.org/D153672

GitOrigin-RevId: b5270ba20dc3d84df9d880be11d57667f04c6c28
57 files changed