arch,cpu,kern,sim: Eliminate the utility.hh switching header.

This header is no longer used. Remove the places where it's included,
and stop generating it. Also eliminate the now empty SPARC and Power
versions of the header.

Change-Id: I6ee66d39bc0218d1d9b9b7db3b350134ef03251d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39337
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/arch/SConscript

@@ -64,7 +64,6 @@ env.SwitchingHeaders(
         registers.hh
         remote_gdb.hh
         types.hh
-        utility.hh
         '''),
     env.subst('${TARGET_ISA}'))