[BP 7.2.5] - XDCR transaction processing does not include DELETION/EXPIRATION

XDCR assumes that deletion/expirations do not have xattrs and do not need xattr processing:

https://github.com/couchbase/goxdcr/blob/122714ca9e3ead4bd43f4989631e479ea5f46d19/base/filter/filterImpl.go#L255

This is an incorrect assumption. Tombstones can have system xattrs (those with _ prefix). Inserts inside a transaction can create tombstones with transaction xattrs.

https://docs.google.com/document/d/1lRC-0VEk4jTPJbY9tN_jHTiqzCbj7Qpt4JdYufwEMwU/edit#heading=h.m48lmw9ahldh 

XDCR should process UPR_DELETION for transactions just like any other mutations.