[buildtools] Add DIR_METADATA files.

Generate DIR_METADATA files
and remove metadata from OWNERS files
for //buildtools.

Bug: 1113033
Change-Id: I54fdf94f060220d189ce9c843e02fc22f12df623
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438877
Commit-Queue: Dirk Pranke <dpranke@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Cr-Commit-Position: refs/heads/master@{#811878}

buildtools/DIR_METADATA

+monorail {
+  component: "Build"
+}
+
+team_email: "build@chromium.org"

buildtools/OWNERS

 dpranke@google.com
 thakis@chromium.org
 thomasanderson@chromium.org
-
-# TEAM: build@chromium.org
-# COMPONENT: Build