select_tx_mode(): remove special case for key frame

This commit removes the special case for key frame, as transform size
decision is controlled by the appropriate speed feature for all lossy
coding modes: tx_size_search_method.

Change-Id: I9677171e3f2432ec23705f7c5ea8170dd4562fae

vp9/encoder/vp9_encodeframe.c

@@ -2603,8 +2603,6 @@ static MV_REFERENCE_FRAME get_frame_type(const VP9_COMP *cpi) {
 static TX_MODE select_tx_mode(const VP9_COMP *cpi) {
   if (cpi->mb.e_mbd.lossless)
     return ONLY_4X4;
-  if (cpi->common.frame_type == KEY_FRAME)
-    return TX_MODE_SELECT;
   if (cpi->sf.tx_size_search_method == USE_LARGESTALL)
     return ALLOW_32X32;
   else if (cpi->sf.tx_size_search_method == USE_FULL_RD||