unix: drop go version tags for unsupported versions

go.mod specifies go 1.18. Drop go1.n version tags for older, unsupported
versions.

Change-Id: I8563bd2cc8e86bd560a45b885a9aa2e6bcc95c47
Reviewed-on: https://go-review.googlesource.com/c/sys/+/559415
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

unix/aliases.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 (aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos) && go1.9
+//go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris || zos
 
 package unix
 

unix/darwin_test.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 darwin && go1.12
+//go:build darwin
 
 package unix
 

unix/dev_linux_test.go

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build go1.7
-
 package unix_test
 
 import (

unix/mkasm.go

@@ -80,7 +80,7 @@ func generateASMFile(goos, arch string, inFileNames []string, outFileName string
 const darwinTestTemplate = `// go run mkasm.go %s
 // Code generated by the command above; DO NOT EDIT.
 
-//go:build darwin && go1.12
+//go:build darwin
 
 package unix
 

unix/syscall_darwin_libSystem.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 darwin && go1.12
+//go:build darwin
 
 package unix