cluster/addons/dashboard: remove inactive members from OWNERS

As a part of cleaning up inactive members (who haven't been active since
beginning of 2019) from OWNERS files, this commit removes konryd and
cheld from the list of reviewers.

Author: nikhita

cluster/addons/dashboard/OWNERS

@@ -6,8 +6,6 @@ approvers:
 - jeefy
 - maciaszczykm
 reviewers:
-- cheld
 - danielromlein
 - ianlewis
-- konryd
 - rf232