Remove left-over populate_io_cache_on_flush and replicate_on_write uses

patch by Aleksey Yeschenko; reviewed by Jonathan Ellis for CASSANDRA-7493
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	doc/cql/CQL.textile
	src/java/org/apache/cassandra/cql/CFPropDefs.java