x86: remove dead writes from setup_mmu()

Recent changes cause end_of_memory to be disregarded in 32-bit. Remove
the dead writes to it.

Signed-off-by: Nadav Amit <namit@vmware.com>
Message-Id: <20200710183320.27266-4-namit@vmware.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>