Update OWNERS from the art-team

Test: build/make/tools/checkowners.py -c -v libcore/OWNERS
Change-Id: If3a4bd700ceb823588cdf404f740f09784542fee
diff --git a/OWNERS b/OWNERS
index 890bf2e..a02f994 100644
--- a/OWNERS
+++ b/OWNERS
@@ -13,7 +13,7 @@
 vichang@google.com
 
 # Don't send these folks any review emails for this project.
+calin@google.com
 narayan@google.com
 ngeoffray@google.com
-sehr@google.com
 vmarko@google.com