Revert "Explicitly use Long.MAX_VALUE timestamp for counter deletions"

This reverts commit 5fe7557627fac6ace2554a4f8ef552c9d9512490.

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	src/java/org/apache/cassandra/cql/AbstractModification.java
	src/java/org/apache/cassandra/cql/DeleteStatement.java
	src/java/org/apache/cassandra/cql/UpdateStatement.java