Remove support for pre 5.3

Change-Id: I5f9a36fb33f145e5fac455d80abbed7b79597d91
Reviewed-on: http://review.couchbase.org/24304
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>