RUBY-1333 Remove broken/redundant tests from topology spec.
RUBY-1333 Remove broken/redundant tests from topology spec.

The "one node replica set" test is contrary to current SDAM behavior
and hence should not ever succeed. I doubt it even runs because
a typical replica set configuration includes more than one node.

The "single mongos" test is redundant with a test above that checks
the exact same thing.

Removing these tests allows using the lite spec helper.

saghm/mongo-ruby-driver,jonhyman/mongo-ruby-driver,mongodb/mongo-ruby-driver,mongodb/mongo-ruby-driver,jonhyman/mongo-ruby-driver,mongodb/mongo-ruby-driver,saghm/mongo-ruby-driver