scons,arch: Remove simple scalar compatibility.

scons,arch: Remove simple scalar compatibility.

This was primarily in Alpha where disassmbly output could be compatible
(default off, probably not usd in a long time), and floating point
could be compatible (default on). A small bit had crept into x86 from
long ago which is also removed.

Change-Id: Ibb68b63787f370259bd1613b393e0b057c007704
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/25012
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Tested-by: kokoro <noreply+kokoro@google.com>