ISPN-4293 PR for ISPN-4137 causes a performance drop in repl tx mode

Local transactions should not be added to the completed txs map.

Unrelated change: In a tx cache, only TransactionBoundaryCommands can
be forwarded to the new owners because of a topology change.
ISPN-4293 PR for ISPN-4131 also caused a perf drop in tx mode

To fix ISPN-4131 we have to keep track of the highest tx id removed from
the completed txs map by the cleanup thread. The initial fix thus required
accessing two maps both to check if a tx was already completed and to mark
a tx as completed.

I was able to eliminate the second map lookup for marking the tx as
completed in the commit command, reducing the overhead somewhat.