Ruby: Simplify tester ports by not using SimpleTimingPort

Ruby: Simplify tester ports by not using SimpleTimingPort

This patch simplfies the master ports used by RubyDirectedTester and
RubyTester by avoiding the use of SimpleTimingPort. Neither tester
made any use of the functionality offered by SimpleTimingPort besides
a trivial implementation of recvFunctional (only snoops) and
recvRangeChange (not relevant since there is only one master).

The patch does not change or add any functionality, it merely makes
the introduction of a master/slave port easier (in a future patch).