cmd/internal/obj/loong64: remove unuseless functions

cmd/internal/obj/loong64: remove unuseless functions

Change-Id: Ieee97a9477090d4273e54a6667b0a051bb0c1e9d
Reviewed-on: https://go-review.googlesource.com/c/go/+/565619
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Qiqi Huang <huangqiqi@loongson.cn>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>