remove bogus extra logic for close cancellability

like all other syscalls, close should return to the caller if and only
if it successfully performed its action. it is necessary that the
application be able to determine whether the close succeeded.

src/unistd/close.c

@@ -4,7 +4,5 @@
 
 int close(int fd)
 {
-	int ret = syscall_cp(SYS_close, fd);
-	if (libc.testcancel) libc.testcancel();
-	return ret;
+	return syscall_cp(SYS_close, fd);
 }