Remove rickywai@google.com from services/core/java/com/android/server/wm/OWNERS

This suggested change is automatically generated based on group
memberships and affiliations.
If this change is unnecessary or in error, vote CR -1 and the bot
will abandon it. Vote CR +1/2 to approve this change.

See the owner's recent activity for context:
https://android-review.googlesource.com/q/rickywai@google.com

To report an issue, file a bug in the Infra>Codereview component.

Change-Id: I5d82a4e061035030c552c082c371b28534f59d08