sim: delete duplicate SIGINT handling

sim: delete duplicate SIGINT handling

Many of the simulators change the SIGINT handler.
E.g., moxie/interp.c:

  sigsave = signal (SIGINT, interrupt);

However, this is unnecessary.
remote-sim.h already provides an API for asynchronously stopping
a sim; and both gdb and the drivers (run.c and nrun.c at least,
I didn't check the others) install a SIGINT handler which
calls this method.

URL: https://sourceware.org/bugzilla/show_bug.cgi?id=16450
Reported-by: Tom Tromey <tromey@redhat.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>