website: Remove incorrect ISA 'ARCH' in building docs

Change-Id: I4d7b1ec074ff0a8d20d9feee31b1b5ed8540ffb3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/55983
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
1 file changed