Revert "move platinum tests from staging to live"

This reverts commit 9eaeaca4efd10f6adba730c1f1636b3ff5c7e529.

Reason for revert: b/157014488

Change-Id: I9c5dd7238860f5b73edfaa120bb965513cec5d3f
diff --git a/media/TEST_MAPPING b/media/TEST_MAPPING
index b006f38..206f87f 100644
--- a/media/TEST_MAPPING
+++ b/media/TEST_MAPPING
@@ -48,7 +48,7 @@
         }
     ],
 
-    "platinum-postsubmit": [
+    "staged-platinum-postsubmit": [
         // runs regularly, independent of changes in this tree.
         // signals if changes elsewhere break media functionality
         {