Revert "chacha20: add loong64 SIMD implementation"

This reverts CL 636257.

Reason for revert: Does not build on 1.23 or 1.24

For golang/go#73354.

Change-Id: Ie28d5c45930a8eacd5cabed64390ef674b3fb446
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/665536
Reviewed-by: abner chenc <chenguoqi@loongson.cn>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

chacha20/chacha_noasm.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (!arm64 && !loong64 && !s390x && !ppc64 && !ppc64le) || !gc || purego
+//go:build (!arm64 && !s390x && !ppc64 && !ppc64le) || !gc || purego
 
 package chacha20