migrations: drop licenses.module_path and licenses.version

These columns are no longer used.

Fixes golang/go#39629

Change-Id: I258103dafe6ce96495a4b59c49d372cea8692486
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/272088
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

migrations/000050_drop_licenses_module_path_version_columns.down.sql

@@ -0,0 +1,11 @@
+-- Copyright 2020 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+ALTER TABLE licenses
+    ADD COLUMN module_path TEXT,
+    ADD COLUMN version TEXT;
+
+END;

migrations/000050_drop_licenses_module_path_version_columns.up.sql

@@ -0,0 +1,11 @@
+-- Copyright 2020 The Go Authors. All rights reserved.
+-- Use of this source code is governed by a BSD-style
+-- license that can be found in the LICENSE file.
+
+BEGIN;
+
+ALTER TABLE licenses
+    DROP COLUMN module_path,
+    DROP COLUMN version;
+
+END;