timeval: Remove backtrace feature.

timeval: Remove backtrace feature.

The backtrace feature of timeval is useful because it provides a "poor
man's profile" view of Open vSwitch.  But it is not likely to be useful in
a multithreaded process, because signal delivery doesn't necessarily follow
the profile when there is more than one thread.  (A signal in a
multithreaded process are delivered to an arbitrary thread.)

Another problem with the backtrace feature is that it is difficult for
format_backtraces() to synchronize properly with the signal handler in a
multithreaded process.  In a single-threaded process, it can just block
the signal handler, but in a multithreaded process this does not prevent
signal delivery to threads other than the one running format_backtrace().

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ed Maste <emaste@freebsd.org>