Deprecate most of debug-memory

Deprecate most of debug-memory

Fixes #8322

The leak-checking (and backtrace option, on some platforms) provided
by crypto-mdebug and crypto-mdebug-backtrace have been mostly neutered;
only the "make malloc fail" capability remains.  OpenSSL recommends using
the compiler's leak-detection instead.

The OPENSSL_DEBUG_MEMORY environment variable is no longer used.
CRYPTO_mem_ctrl(), CRYPTO_set_mem_debug(), CRYPTO_mem_leaks(),
CRYPTO_mem_leaks_fp() and CRYPTO_mem_leaks_cb() return a failure code.
CRYPTO_mem_debug_{malloc,realloc,free}() have been removed.  All of the
above are now deprecated.

Merge (now really small) mem_dbg.c into mem.c

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10572)