Revert "Add an internal notice file for internal checkouts."

This reverts commit 370d4e3a61ecf6c153cdafe05a21bd3037ed67a6.

Reason for revert: this method doesn't work.

Change-Id: Id873ff0c76a901b27c4139821b7e62d9986a496e
diff --git a/.INTERNAL_NOTICE.md b/.INTERNAL_NOTICE.md
deleted file mode 100644
index 467e71c..0000000
--- a/.INTERNAL_NOTICE.md
+++ /dev/null
@@ -1,3 +0,0 @@
-This file is used to warn developers of internal code checkouts. If you are
-reading this, don't be worried -- external contributors only see the OSS
-repositories, and you're safe.