Remove test_synchronization.

The assertions that this test makes are basically nonsense; actions are
not "synchronized" with the main thread in any meaningful way.

I suspect that when this test was written, its author (probably me) just
didn't understand threads very well.

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/branches/desynchronize-2673@43159 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb