SyncDeletes do not update maxDelRevSeqno, which can cause rev ids to go backwards

Spin out of a customer issue where they were seeing redid go backwards.

Thanks to Graham Pople providing a reproduction.

James Lee kindly converted it to "go" version, which I have attached

It performs 3 operations on the same key - "daniel". The operations and rev id is as follows:

standard set
rev_id: 1
majority sync-write delete
rev_id: 2
majority sync-write set
rev_id: 1

(Note the key is "daniel" which corresponds to vbucket 644)

Worth noting that all non-sync operations work as expected e.g.
standard set
rev_id: 1
standard delete
rev_id: 2
standard set
rev_id: 3

Also the following works as expected e.g.
standard set
rev_id: 1
standard delete
rev_id: 2
majority sync-write set
rev_id: 3

However the following breaks
standard set
rev_id: 1
majority sync-write delete
rev_id: 2
standard set
rev_id: 1

So the issue appears to be with sync-write delete