Remove no longer used checkpoint logic

This is not longer useful as of MB-7413. After each large batch
is applied a checkpoint is always performed.

Change-Id: I203c6192b9e2a763c9844b868e8de16d5781922f
Reviewed-on: http://review.couchbase.org/25011
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>