main: Remove old style build constraints.

This removes the old style build constraints that were required for
versions of Go prior to version 1.17 now that only Go 1.18 and Go 1.19
are actively supported.

Note that it intentionally does not remove them from the modules to
avoid needlessly breaking any consumers that might still be using them
form older versions of Go.

internal/integration/rpctests/rpcserver_test.go

@@ -6,7 +6,6 @@
 
 // This file is ignored during the regular tests due to the following build tag.
 //go:build rpctest
-// +build rpctest
 
 package rpctests
 

internal/integration/rpctests/treasury_test.go

@@ -5,7 +5,6 @@
 
 // This file is ignored during the regular tests due to the following build tag.
 //go:build rpctest
-// +build rpctest
 
 package rpctests
 

internal/limits/limits_unix.go

@@ -4,7 +4,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows && !plan9
-// +build !windows,!plan9
 
 package limits
 

internal/limits/memlimit.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build go1.19
-// +build go1.19
 
 package limits
 

internal/limits/memlimit_old.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !go1.19
-// +build !go1.19
 
 package limits
 

internal/version/version_buildinfo.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build go1.18
-// +build go1.18
 
 package version
 

internal/version/version_nobuildinfo.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !go1.18
-// +build !go1.18
 
 package version
 

signal_syscall.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 //
 //go:build windows || aix || android || darwin || dragonfly || freebsd || hurd || illumos || ios || linux || netbsd || openbsd || solaris
-// +build windows aix android darwin dragonfly freebsd hurd illumos ios linux netbsd openbsd solaris
 
 package main