cmd/link/internal/loadelf: remove useless relocation size information of loong64

cmd/link/internal/loadelf: remove useless relocation size information of loong64

As of CL 455017 we have switched to following the new style relocations on
loong64, these stack based relocations should be removed.

Change-Id: Ic129a5665cf6f183a32e13b6f1a55d712a99d721
Reviewed-on: https://go-review.googlesource.com/c/go/+/537335
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: abner chenc <chenguoqi@loongson.cn>
Commit-Queue: abner chenc <chenguoqi@loongson.cn>
Reviewed-by: Qiqi Huang <huangqiqi@loongson.cn>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>