Dropping errant RPORT required option for UDP

MSP-11652
RPORT is required by UDPScanner; deregister instead
Merge pull request #1 from jhart-r7/landing-4265-jhart

This is a great intermediate approach, thanks @jhart-r7 ! Will verify Pro and msfconsole cases momentarily.
Land #4265, @shuckins-r7 fix for RPORT error on UDP sweep.