Improve "replSet too much data to roll back" to include reason for "too much data" limit

There are two methods used for rollback:
1. "Rollback to Timestamp" (default)
2. "Rollback-via-Refetch" - used when "enableMajorityReadConcern=false"

Under condition #1 the 300MB rollback limit is no longer enforced post-4.0. But under condition #2, the limit is still enforced, and users can still get the following assertions:

2020-05-03T00:11:01.079Z F -        [rsBackgroundSync] Fatal Assertion 40507 at src/mongo/db/repl/rs_rollback.cpp 1515

2020-05-03T00:11:01.079Z F ROLLBACK [rsBackgroundSync] Unable to complete rollback. A full resync may be needed: UnrecoverableRollbackError: replSet too much data to roll back.

It would be helpful to include the information that the rollback limit was enforced because "enableMajorityReadConcern=false".