MB-13011: Refactor DELETE to permit an extras section

Similar to the previous arithmetic change, allow the DELETE binary
protocol response to include an extras section containing the vBucket
UUID and sequence number for the delete operation.

Note that memcached does *not* yet populate the vbucket UUID/seqno
pair; currently they have placeholder values.

Change-Id: Ida604c899587c04b4c60dc835852bdce1761e20d
Reviewed-on: http://review.couchbase.org/44756
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>