Do not print backtraces on fatal glibc errors

If the process is in a bad state, we used to print backtraces in
many cases.  This is problematic because doing so could involve
a lot of work, like loading libgcc_s using the dynamic linker,
and this could itself be targeted by exploit writers.  For example,
if the crashing process was forked from a long-lived process, the
addresses in the error message could be used to bypass ASLR.

Commit ed421fca ("Avoid backtrace from
__stack_chk_fail [BZ #12189]"), backtraces where no longer printed
because backtrace_and_maps was always called with do_abort == 1.

Rather than fixing this logic error, this change removes the backtrace
functionality from the sources.  With the prevalence of external crash
handlers, it does not appear to be particularly useful.  The crash
handler may also destroy useful information for debugging.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>