Fix upgrade tool

cmd/upgrade/package.go

@@ -1,11 +0,0 @@
-// Copyright (C) 2018 The Go-SQLite3 Authors.
-//
-// Use of this source code is governed by an MIT-style
-// license that can be found in the LICENSE file.
-//
-// Dummy to ensure package can be loaded
-//
-// This file is to avoid the following error:
-// can't load package: package go-sqlite3/upgrade: build constraints exclude all Go files in tools/upgrade
-
-package main

cmd/upgrade/upgrade.go

@@ -3,9 +3,6 @@
 // Use of this source code is governed by an MIT-style
 // license that can be found in the LICENSE file.
 
-// +build !cgo
-// +build upgrade
-
 package main
 
 import (