Remove obsolete TODO.

MRC_TX experiment was abandoned for AV1

Change-Id: I22a01e9421f2fa75c94218419a53d9d726a9332d
diff --git a/av1/common/enums.h b/av1/common/enums.h
index 88a7bb0..bb0dafa 100644
--- a/av1/common/enums.h
+++ b/av1/common/enums.h
@@ -259,8 +259,6 @@
   ADST_1D,
   FLIPADST_1D,
   IDTX_1D,
-  // TODO(sarahparker) need to eventually put something here for the
-  // mrc experiment to make this work with the ext-tx pruning functions
   TX_TYPES_1D,
 } TX_TYPE_1D;