all: update go directive to 1.18

Done with:

go get [email protected]
go mod tidy
go fix ./...

Using go1.21.3.

Also update avo to v0.5.0 in the curve25519/internal/field/_asm module.
It's newer and produces no diff in the generated code.

For golang/go#60268.

Change-Id: I9bd771ee8561595d7f68aaca76df6e3e33d35013
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/534141
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: dmitshur

acme/version_go112.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build go1.12
-// +build go1.12
 
 package acme
 

argon2/blamka_amd64.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build amd64 && gc && !purego
-// +build amd64,gc,!purego
 
 package argon2
 

argon2/blamka_amd64.s

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build amd64 && gc && !purego
-// +build amd64,gc,!purego
 
 #include "textflag.h"
 

argon2/blamka_ref.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !amd64 || purego || !gc
-// +build !amd64 purego !gc
 
 package argon2
 

blake2b/blake2bAVX2_amd64.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build go1.7 && amd64 && gc && !purego
-// +build go1.7,amd64,gc,!purego
 
 package blake2b
 

blake2b/blake2bAVX2_amd64.s

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build go1.7 && amd64 && gc && !purego
-// +build go1.7,amd64,gc,!purego
 
 #include "textflag.h"
 

blake2b/blake2b_amd64.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !go1.7 && amd64 && gc && !purego
-// +build !go1.7,amd64,gc,!purego
 
 package blake2b
 

blake2b/blake2b_amd64.s

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build amd64 && gc && !purego
-// +build amd64,gc,!purego
 
 #include "textflag.h"
 

blake2b/blake2b_ref.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !amd64 || purego || !gc
-// +build !amd64 purego !gc
 
 package blake2b
 

blake2b/register.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build go1.9
-// +build go1.9
 
 package blake2b