Remove mdbooth as a maintainer

Author: mdbooth

OWNERS_ALIASES

@@ -21,7 +21,7 @@ aliases:
   cluster-api-openstack-maintainers:
     - emilienm
     - lentzi90
-    - mdbooth
   cluster-api-openstack-reviewers:
   cluster-api-openstack-emeritus-maintainers:
     - jichenjc
+    - mdbooth