Move ART run-tests to the `postsubmit` test group in `TEST_MAPPING`.

Test: atest --test-mapping art:postsubmit
Test: Check Android post-submit testing results
Bug: 152374989
Change-Id: If60ba4a3179f58d33e69872cd4016b827744e16f
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 97e76f7..c6b0f55 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -6,11 +6,11 @@
     }
   ],
   "postsubmit": [
+    // ART gtests.
     {
       "name": "ArtGtestsTarget"
-    }
-  ],
-  "art-run-tests": [
+    },
+    // ART run-tests.
     {
       "name": "art-run-test-001-HelloWorld"
     },
diff --git a/test/utils/regen-test-files b/test/utils/regen-test-files
index 9572045..aa5cbe9 100755
--- a/test/utils/regen-test-files
+++ b/test/utils/regen-test-files
@@ -342,11 +342,11 @@
     }
   ],
   "postsubmit": [
+    // ART gtests.
     {
       "name": "ArtGtestsTarget"
-    }
-  ],
-  "art-run-tests": [
+    },
+    // ART run-tests.
 EOF
 # Only include tests expected to succeed for now.
 trailer=,