version: simplify iOS detection now that we require Go 1.16

See https://golang.org/doc/go1.16#darwin

No need for build tag tricks anymore.

version/prop.go

@@ -8,15 +8,13 @@ import "runtime"
 
 // IsMobile reports whether this is a mobile client build.
 func IsMobile() bool {
-	// Good enough heuristic for now, at least until Apple makes
-	// ARM laptops...
-	return runtime.GOOS == "android" || isIOS
+	return runtime.GOOS == "android" || runtime.GOOS == "ios"
 }
 
 // OS returns runtime.GOOS, except instead of returning "darwin" it
 // returns "iOS" or "macOS".
 func OS() string {
-	if isIOS {
+	if runtime.GOOS == "ios" {
 		return "iOS"
 	}
 	if runtime.GOOS == "darwin" {

version/prop_ios.go

@@ -1,9 +0,0 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build ios
-
-package version
-
-const isIOS = true

version/prop_notios.go

@@ -1,9 +0,0 @@
-// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build !ios
-
-package version
-
-const isIOS = false