Remove unused code initially produced for MB-8689

Not used anymore. A different solution was implemented, in which
database compaction does not purge deleted documents with sequence
numbers higher than the ones last processed for all indexes.

Change-Id: Iae4d9f7c4d934954ca86e4c4babaa4a0e16fab37
Reviewed-on: http://review.couchbase.org/28430
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>