Integrate and remove Clang hardening instructions

The file contrib/clang/sanitize_blacklist.txt contains instructions on how to build Tor with AddressSanitizer using Clang. Recent changes to the build system made most of these instructions obsolete (see #13538 (moved), #18934 (moved), #18841 (moved)).

FWICT the only thing that is not implemented are some CFLAGS and LDFLAGS options.