cql3: fix deciding if a query uses indexing
cql3: fix deciding if a query uses indexing

The code that decides whether a query should used indexing
was buggy - a partition key index might have influenced the decision
even if the whole partition key was passed in the query (which
effectively means that indexing it is not necessary).

Fixes #4539

avikivity/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla