With the presence of sequence number, we no longer use versionType to
resolve out of order collision in replication and recovery requests.
However, we can only remove the versionType from translog in 7.0+ as it
is required in a mixed cluster between 6.x and 5.x.

This change relaxes the versionType check when comparing two translog
operations so that a 6.x can work with a 7.x (without versionType).