Allow CQL queries on multiple indexes without ALLOW FILTERING

The Index Group index was added by CASSANDRA-16092 to allow indexes to be grouped and have more than one index expression in a query. This did not make any changes to StatementRestrictions so CQL queries using multiple index expression still need to add ALLOW FILTERING to the query to be valid.

This restriction should be removed such that any number of index expressions can be used on a CQL query without needing ALLOW FILTERING.