Move manifest config logic into ManifestProject

Use ManifestProject properties for config values.

Change-Id: Ib4ad90b0d9a089916e35615b8058942e6d01dc04
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/334519
Tested-by: LaMont Jones <lamontjones@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
diff --git a/git_superproject.py b/git_superproject.py
index 299d253..f4dbb27 100644
--- a/git_superproject.py
+++ b/git_superproject.py
@@ -406,7 +406,7 @@
   if opt.use_superproject is not None:
     return opt.use_superproject
   else:
-    client_value = manifest.manifestProject.config.GetBoolean('repo.superproject')
+    client_value = manifest.manifestProject.use_superproject
     if client_value is not None:
       return client_value
     else: