Remove legacy +build: constraint (#19582)

Go 1.17 and later use modern `//go:build` constraints, the old `// +build:` constraints should be removed.

modules/graceful/manager_unix.go

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

modules/graceful/manager_windows.go

@@ -4,7 +4,6 @@
 // This code is heavily inspired by the archived gofacebook/gracenet/net.go handler
 
 //go:build windows
-// +build windows
 
 package graceful
 

modules/graceful/net_unix.go

@@ -4,7 +4,6 @@
 // This code is heavily inspired by the archived gofacebook/gracenet/net.go handler
 
 //go:build !windows
-// +build !windows
 
 package graceful
 

modules/graceful/net_windows.go

@@ -4,7 +4,6 @@
 // This code is heavily inspired by the archived gofacebook/gracenet/net.go handler
 
 //go:build windows
-// +build windows
 
 package graceful
 

modules/graceful/restart_unix.go

@@ -4,7 +4,6 @@
 // This code is heavily inspired by the archived gofacebook/gracenet/net.go handler
 
 //go:build !windows
-// +build !windows
 
 package graceful