stats: Get rid of some kernel stats related cruft.

The kernel stat mechanism should really be refactored and moved somewhere
else, but in the mean time there's some old cruft that can be cleared away.

Change-Id: I21e725de590dda0d20bf3bc675bbe976c7b1bd86
Reviewed-on: https://gem5-review.googlesource.com/4600
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

Make commenting on close namespace brackets consistent.

Ran all the source files through 'perl -pi' with this script:

s|\s*(};?\s*)?/\*\s*(end\s*)?namespace\s*(\S+)\s*\*/(\s*})?|} // namespace $3|;
s|\s*};?\s*//\s*(end\s*)?namespace\s*(\S+)\s*|} // namespace $2\n|;
s|\s*};?\s*//\s*(\S+)\s*namespace\s*|} // namespace $1\n|;

Also did a little manual editing on some of the arch/*/isa_traits.hh files
and src/SConscript.

Put kernel_stats back into arch.