runtime: remove stray errno check from TestSignalM

CL 206078 introduced a stray errno check that was always false. This CL removes it.

Updates #35276

Change-Id: I6996bb595d347fe81752786a3d83d3432735c9cb
GitHub-Last-Rev: e026e71b16c8532ad707a0b43b4f02c7a366257e
GitHub-Pull-Request: golang/go#35650
Reviewed-on: https://go-review.googlesource.com/c/go/+/207577
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/crash_unix_test.go

@@ -326,13 +326,9 @@ func TestSignalM(t *testing.T) {
 	wg.Add(1)
 	go func() {
 		runtime.LockOSThread()
-		var errno int32
 		want, got = runtime.WaitForSigusr1(r, w, func(mp *runtime.M) {
 			ready <- mp
 		})
-		if errno != 0 {
-			t.Error(syscall.Errno(errno))
-		}
 		runtime.UnlockOSThread()
 		wg.Done()
 	}()