crimson/common: let's dump the core on fatal signal.

Removing the call to engine's `exit()` should allow the singnal
handler to exit. In the case of `SIGSEGV` this would return back
to the problematic instruction, and thus retrigger the fault.
As our handler already restores `SIG_DFL`, it's expected to get
a core dump.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>

src/crimson/common/fatal_signal.cc

@@ -58,5 +58,4 @@ void FatalSignal::signaled(int signum)
     break;
   }
   signal(signum, SIG_DFL);
-  seastar::engine().exit(1);
 }