Add DIR_METADATA files to //mojo

Add Generate DIR_METADATA files and remove metadata from OWNERS
files for //mojo.

R=rockot@google.com

Bug: 1113033
Change-Id: I6e12b602687b803c0270c86a0df3771b74c2e081
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2454408
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#814680}

mojo/DIR_METADATA

+# Metadata information for this directory.
+#
+# For more information on DIR_METADATA files, see:
+#   https://source.chromium.org/chromium/infra/infra/+/master:go/src/infra/tools/dirmd/README.md
+#
+# For the schema of this file, see Metadata message:
+#   https://source.chromium.org/chromium/infra/infra/+/master:go/src/infra/tools/dirmd/proto/dir_metadata.proto
+
+monorail {
+  component: "Internals>Mojo"
+}
\ No newline at end of file

mojo/OWNERS

@@ -5,5 +5,3 @@ sky@chromium.org
 
 # For Fuchsia-specific changes:
 per-file *_fuchsia*=file://build/fuchsia/OWNERS
-
-# COMPONENT: Internals>Mojo