Enable ntpq tests on Windows (#3972)

Makefile

@@ -60,6 +60,7 @@ test-windows:
 	go test ./plugins/inputs/win_perf_counters/...
 	go test ./plugins/inputs/win_services/...
 	go test ./plugins/inputs/procstat/...
+	go test ./plugins/inputs/ntpq/...
 
 # vet runs the Go source code static analysis tool `vet` to find
 # any common errors.

plugins/inputs/ntpq/ntpq_test.go

-// +build !windows
-
 package ntpq
 
 import (