Remove /qemu from EC2 ARM AMIs

I forgot to do this as part of r345858 -- I added it to the
vm_extra_pre_umount in vmimage.subr but forgot that function
was overridden in the EC2 build.

MFC after:	2 weeks

release/tools/ec2.conf

@@ -116,6 +116,9 @@ vm_extra_pre_umount() {
 	# * firstboot_pkgs (install packages)
 	touch ${DESTDIR}/firstboot
 
+	if ! [ -z "${QEMUSTATIC}" ]; then
+		rm -f ${DESTDIR}/${EMULATOR}
+	fi
 	rm -f ${DESTDIR}/etc/resolv.conf
 
 	return 0