Prune root OWNERs file to better assign reviews. (kubeflow#3231)

* Prune root OWNERs file to better assign reviews.

* ellis-biegelow is being assigned a lot of reviews because we are hitting
  the root OWNERs file.

* Remove @r2d4 since the goal is to prune the set of approvers.

Author: jlewi

OWNERS

@@ -1,13 +1,9 @@
-# TODO(jlewi): We should probably have OWNERs files in subdirectories that
-# list approvers for individual components (e.g. Seldon folks for Seldon component)
+# We want to rely on fine grained OWNERs files.
+# Approvers listed here is just a backup in case someone is out.
 approvers:
   - abhi-g
   - jlewi
   - kunmingg
   - lluunn
   - pdmack
-  - r2d4
   - richardsliu
-  - texasmichelle
-reviewers:
-  - ellis-bigelow