database/{query,query_mutations}: don't rethrow read semaphore exceptions
database/{query,query_mutations}: don't rethrow read semaphore exceptions

Now, read semaphore exceptions are propagated from database::query and
database::query_mutations without rethrowing them.

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