test(signal): remove unnecessary syscall

The test issues a "forbidden" syscall, but the seccomp filters are not
enabled, so it does nothing.
I tried to replace it with SIGSYS to assert that the corresponding
metric is emitted, but it crashed the test, so I'm just removing it.

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

src/vmm/src/signal_handler.rs

@@ -185,9 +185,6 @@ mod tests {
         let child = thread::spawn(move || {
             register_signal_handlers().unwrap();
 
-            // Call the forbidden `SYS_mkdirat`.
-            unsafe { libc::syscall(libc::SYS_mkdirat, "/foo/bar\0") };
-
             // Call SIGBUS signal handler.
             assert_eq!(METRICS.signals.sigbus.fetch(), 0);
             unsafe {