all: simplify build tags involving iOS

Prior to Go 1.16, iOS used GOOS=darwin,
so we had to distinguish macOS from iOS during GOARCH.

We now require Go 1.16 in our go.mod, so we can simplify.

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

portlist/netstat.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 (go1.16 && !ios) || (!go1.16 && !darwin) || (!go1.16 && !arm64)
-// +build go1.16,!ios !go1.16,!darwin !go1.16,!arm64
+//go:build !ios
+// +build !ios
 
 package portlist
 

portlist/netstat_exec.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 (windows || freebsd || openbsd || (darwin && go1.16) || (darwin && !go1.16 && !arm64)) && !ios
-// +build windows freebsd openbsd darwin,go1.16 darwin,!go1.16,!arm64
+//go:build (windows || freebsd || openbsd || darwin) && !ios
+// +build windows freebsd openbsd darwin
 // +build !ios
 
 package portlist

portlist/portlist_ios.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 (go1.16 && ios) || (!go1.16 && darwin && !amd64)
-// +build go1.16,ios !go1.16,darwin,!amd64
+//go:build ios
+// +build ios
 
 package portlist
 

portlist/portlist_macos.go

@@ -2,9 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build ((darwin && amd64 && !go1.16) || (darwin && go1.16)) && !ios
-// +build darwin,amd64,!go1.16 darwin,go1.16
-// +build !ios
+//go:build darwin
+// +build darwin
 
 package portlist
 

version/cmdname.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 (go1.16 && !ios) || (!go1.16 && !darwin) || (!go1.16 && !arm64)
-// +build go1.16,!ios !go1.16,!darwin !go1.16,!arm64
+//go:build !ios
+// +build !ios
 
 package version
 

version/cmdname_ios.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 (go1.16 && ios) || (!go1.16 && darwin && arm64)
-// +build go1.16,ios !go1.16,darwin,arm64
+//go:build ios
+// +build ios
 
 package version