MB-12063 Don't delete expired items during warmup.

When a node is added back to the cluster, its vbucket states
can be different from its previous states (e.g., active -> replica).
Therefore, we should not remove expired items from active vbuckets
during warmup because the states of those vbuckets can be changed
after the warmup.

Change-Id: Ifec4fda80e424a8afa74bae66e17de77b2e0c36b
Reviewed-on: http://review.couchbase.org/41219
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>