x86/mm/shadow: remove dead code for avoiding Xen entries on 32-bit tables.

x86/mm/shadow: remove dead code for avoiding Xen entries on 32-bit tables.

All non-external-mode (==PV) guests have 4-level pagetables now that
the PAE build of Xen is gone.

This patch should have no effect, since the condition it removes could
never be true anyway: the l2 offset of HYPERVISOR_VIRT_START on 64-bit
Xen is much higher than any l2 offset we could have seen in the
tables (and indeed bigger than the 'int' type, which clang was
complaining about).  Actual compat PV guest xen entries are handled by
the equivalent test in the 64-bit SHADOW_FOREACH_L2E() below.

Reported-by: Julien Grall <julien.grall@linaro.org>
Signed-off-by: Tim Deegan <tim@xen.org>