Remove the ignore for the top level .packages file.

Change-Id: Iab05d3658f802615c3cfa6ed921ca7296e8343f0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/249726
Reviewed-by: Kevin Moore <kevmoo@google.com>
Commit-Queue: Devon Carew <devoncarew@google.com>
diff --git a/.gitignore b/.gitignore
index 9c674bd..9bd1379 100644
--- a/.gitignore
+++ b/.gitignore
@@ -75,9 +75,8 @@
 packages
 pubspec.lock
 
-# The top level package files (these are auto-generated per checkout)
+# The top level package file (this is auto-generated per checkout).
 /.dart_tool/package_config.json
-/.packages
 
 # Local pub storage
 .pub