Revert r61650; the intent of this commit was to try and address alarm failures…

Revert r61650; the intent of this commit was to try and address alarm failures on some of the build slaves.  As Neal points out, it's called after test_main(), so it's not going to factor into the test when run via regrtest.py (and removes the original functionality that Jeffrey wanted that would kill the test if it took longer than 3 seconds to run when executing it directly during development).

Lib/test/test_socketserver.py

@@ -253,7 +253,4 @@ def test_main():
 
 if __name__ == "__main__":
     test_main()
-    # Signal an alarm after 20 seconds if we haven't shut down.  This
-    # was originally 3 seconds, but has been bumped as numerous build
-    # slaves have been failing with SIGALMs on this test.
-    signal_alarm(20)
+    signal_alarm(3)  # Shutdown shouldn't take more than 3 seconds.