Fix stale prediction mode names in comments.

In intra_mode_to_tx_type(), the _intra_mode_to_tx_type table has four
comments that use the old prediction mode names (angles). Those
prediction mode names were changed in
commit 69ae7b866dc11abde8cbbc4ff197d446cfb3e2d9:
https://aomedia-review.googlesource.com/c/aom/+/47581

This CL not only updates those comments but also changes all comments to
use the full mode names (rather than just the prefixes), so that the
comments won't be missed in a global find-and-replace if the mode names
are ever changed again.

BUG=aomedia:2235

Change-Id: I3ecf0255b343b1f23f3bef1efad44511920f108d
diff --git a/av1/common/blockd.h b/av1/common/blockd.h
index 2aaf0c0..8555ef0 100644
--- a/av1/common/blockd.h
+++ b/av1/common/blockd.h
@@ -649,19 +649,19 @@
 static TX_TYPE intra_mode_to_tx_type(const MB_MODE_INFO *mbmi,
                                      PLANE_TYPE plane_type) {
   static const TX_TYPE _intra_mode_to_tx_type[INTRA_MODES] = {
-    DCT_DCT,    // DC
-    ADST_DCT,   // V
-    DCT_ADST,   // H
-    DCT_DCT,    // D45
-    ADST_ADST,  // D135
-    ADST_DCT,   // D117
-    DCT_ADST,   // D153
-    DCT_ADST,   // D207
-    ADST_DCT,   // D63
-    ADST_ADST,  // SMOOTH
-    ADST_DCT,   // SMOOTH_V
-    DCT_ADST,   // SMOOTH_H
-    ADST_ADST,  // PAETH
+    DCT_DCT,    // DC_PRED
+    ADST_DCT,   // V_PRED
+    DCT_ADST,   // H_PRED
+    DCT_DCT,    // D45_PRED
+    ADST_ADST,  // D135_PRED
+    ADST_DCT,   // D113_PRED
+    DCT_ADST,   // D157_PRED
+    DCT_ADST,   // D203_PRED
+    ADST_DCT,   // D67_PRED
+    ADST_ADST,  // SMOOTH_PRED
+    ADST_DCT,   // SMOOTH_V_PRED
+    DCT_ADST,   // SMOOTH_H_PRED
+    ADST_ADST,  // PAETH_PRED
   };
   const PREDICTION_MODE mode =
       (plane_type == PLANE_TYPE_Y) ? mbmi->mode : get_uv_mode(mbmi->uv_mode);