arch: Remove the stacktrace.hh switching header file.

This is no longer used.

Change-Id: I1419b28d51ff603beb7d8ab89632ad7038c3057e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32215
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/SConscript

@@ -65,7 +65,6 @@ env.SwitchingHeaders(
         pseudo_inst.hh
         registers.hh
         remote_gdb.hh
-        stacktrace.hh
         types.hh
         utility.hh
         '''),