Remove extraneous 'thrift' dependency

The `thrift` dependency was introduced in b45e4d03d777c672c8870dfcc0dea186db4e6b94 but I removed the `erlcassa` dependency in 80a802b4be52c92612a4d20bb246c00a78625937.

Not making this change could actually cause `basho_bench_driver_cassandra.erl` to break if the code path search order is ever changed as both `thrift` and `casbench` include a `thrift_client.erl` module with different implementations. It just happens that `casbench`'s one is actually used and is first on the path.