chacha20: drop Go 1.10 compatibility for arm64

Other packages already dropped compatibility with go < 1.12, so it should be safe to remove it for this package as well.

Change-Id: Ib1424763e3aa94d0187a667ebee058100136f53b
GitHub-Last-Rev: 51df969
GitHub-Pull-Request: #241
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/448241
Reviewed-by: Roland Shoemaker <[email protected]>
Auto-Submit: Filippo Valsorda <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Roland Shoemaker <[email protected]>
Reviewed-by: Filippo Valsorda <[email protected]>
Reviewed-by: Joedian Reid <[email protected]>

Author: thaJeztah

chacha20/chacha_arm64.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.11 && gc && !purego
-// +build go1.11,gc,!purego
+//go:build gc && !purego
+// +build gc,!purego
 
 package chacha20
 

chacha20/chacha_arm64.s

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.11 && gc && !purego
-// +build go1.11,gc,!purego
+//go:build gc && !purego
+// +build gc,!purego
 
 #include "textflag.h"
 

chacha20/chacha_noasm.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (!arm64 && !s390x && !ppc64le) || (arm64 && !go1.11) || !gc || purego
-// +build !arm64,!s390x,!ppc64le arm64,!go1.11 !gc purego
+//go:build (!arm64 && !s390x && !ppc64le) || !gc || purego
+// +build !arm64,!s390x,!ppc64le !gc purego
 
 package chacha20