cmd/link/internal: remove trampoline for plt on loong64

cmd/link/internal: remove trampoline for plt on loong64

When trampoline is called, the plt symbol has not been
added. If we add tramp here, plt will not work.

Change-Id: I64e5d2be9e08f78ca5e8a9dcb267620a481d4416
Reviewed-on: https://go-review.googlesource.com/c/go/+/654918
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: abner chenc <chenguoqi@loongson.cn>