git_superproject: don't filter rewritten manifest

When creating the superproject manifest, take all groups
from the original manifest, including notdefault.

Using the ManifestGroupsStr will inadvertantly filter out
notdefault projects from the superproject manifest.

Change-Id: If3daf41e9a6572348de9182fe8679b90d3cec833
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/610021
Commit-Queue: Andrew Chant <achant@google.com>
Tested-by: Andrew Chant <achant@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>

git_superproject.py

@@ -473,7 +473,7 @@ class Superproject:
             )
             return None
         manifest_str = self._manifest.ToXml(
-            filter_groups=self._manifest.GetManifestGroupsStr(),
+            filter_groups="all",
             omit_local=True,
         ).toxml()
         manifest_path = self._manifest_path