Remove intermittently failing keys fsm test

The keys_fsm_eqc has been intermittently failing for some time. The test
seems to only fail while run under the entire suite. This, along with
discussion in #649 and basho/riak_test#372, it has been determined to
remove this test and write a proper integration test in riak_test.
basho/riak_test#372 will track the progress of this riak_test.

Fixes #899