all: remove old +build tags

The //go:build syntax was introduced in Go 1.17:

https://go.dev/doc/go1.17#build-lines

gofmt has kept the +build and go:build lines in sync since
then, but enough time has passed. Time to remove them.

Done with:

    perl -i -npe 's,^// \+build.*\n,,' $(git grep -l -F '+build')

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tstest/archtest/qemu_test.go

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

tstest/integration/gen_deps.go

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

tstest/integration/vms/dns_tester.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build ignore
-// +build ignore
 
 // Command dns_tester exists in order to perform tests of our DNS
 // configuration stack. This was written because the state of DNS

tstest/integration/vms/harness_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows
-// +build !windows
 
 package vms
 

tstest/integration/vms/nixos_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows
-// +build !windows
 
 package vms
 

tstest/integration/vms/top_level_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows
-// +build !windows
 
 package vms
 

tstest/integration/vms/udp_tester.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build ignore
-// +build ignore
 
 // Command udp_tester exists because all of these distros being tested don't
 // have a consistent tool for doing UDP traffic. This is a very hacked up tool

tstest/integration/vms/vm_setup_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows
-// +build !windows
 
 package vms
 

tstest/integration/vms/vms_steps_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows
-// +build !windows
 
 package vms
 

tstest/integration/vms/vms_test.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows
-// +build !windows
 
 package vms
 

tstest/iosdeps/iosdeps_test.go

@@ -6,7 +6,6 @@
 // worry about "go.exe" etc.
 
 //go:build !windows
-// +build !windows
 
 package iosdeps
 

tstest/jsdeps/jsdeps_test.go

@@ -6,7 +6,6 @@
 // worry about "go.exe" etc.
 
 //go:build !windows
-// +build !windows
 
 package jsdeps
 

tstest/tools/tools.go

@@ -6,7 +6,6 @@
 // tool modules from our go.mod.
 
 //go:build tools
-// +build tools
 
 package tools