Delete ContentHandlerFactoryTest.

It uses reflection, has all sorts of weird stuff in it and isn't
run as part of CTS because it has irreversible side effects (the
last of these isn't the tests fault).

There's no good reason to keep it, and it seems infeasible to write
a half-decent test without adding lots of hidden api (which defeats
the purpose of the test in the first place).

bug: 18619181
Change-Id: I1507a42e12210869b727f46b543e0cebfc50f184