x86: Delegate process loading to the EmuLinux workload.

x86: Delegate process loading to the EmuLinux workload.

This is still triggered by the generic mechanism that tries out all
paths to go from an object file to a process. That's not entirely
necessary since the only loader that should be used when using the
X86ISA::EmuLinux workload is the one it provides, but the rest of gem5
isn't ready for that change yet.

This removes the last lingering reason to keep around the
arch/x86/linux/process.(hh|cc) files, so they have been deleted.

Change-Id: I425b95c9c730f31291790d63bc842e2c0092960d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33904
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Alexandru Duțu <alexandru.dutu@amd.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>