remove some of the uses of wrmask (redundant)

remove some of the uses of wrmask (redundant)
https://bugs.libre-soc.org/show_bug.cgi?id=742

in MultiCompUnit, wrmask is the amalgamation of the incoming "data ok"
signals from an ALU.  ALUs are given the *option* to write to registers:
they are not told, "you absolutely have to write to this register"
but of course for Hazard purposes, the MultiCompUnit has to be told
to "hold" off the write until such time as the ALU can determine whether
it has anything to write

it _should_ now be possible for the ReservationStation version of
FunctionUnit to use combinatorial-setting of write data+ok