Move libc_logging to libasync_safe.

Move the name of the "private/libc_logging.h" header to <async_safe/log.h>.

For use of libc_malloc_debug_backtrace, remove the libc_logging library.
The library now includes the async safe log functions.

Remove the references to libc_logging.cpp in liblog, it isn't needed because
the code is already protected by a check of the __ANDROID__ define.

Test: Compiled and boot bullhead device.
Test: Run debuggerd unit tests.
Test: Run liblog unit tests on target and host.
Test: Run libmemunreachable unit tests (these tests are flaky though).
Change-Id: Ie79d7274febc31f210b610a2c4da958b5304e402