cmd/compile: remove most uses of duintxx

cmd/compile: remove most uses of duintxx

The only remaining uses of duintxx
are in the implementation of duintNN.
I hope to inline those once I figure out why
CL 40864 is broken.

Note that some uses of duintxx with width Widthint
were converted into duintptr.
I did that, since #19954 is officially going to move forward.

Passes toolstash-check.

Change-Id: Id25253b711ea589d0199b51be9a3c18ca1af59ce
Reviewed-on: https://go-review.googlesource.com/41398
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>