Transform search skipping for screen content

Allowed more transform search skipping for screen content at speed 3.
For screen contents, this speed feature actually gave a slight quality
gain(0.08%) with slight speed slow down(0.38%), but tradeoff was good.
TODO: Need to re-evaluate this feature for non-screen contents to check
its performance.

BUG=aomedia:2711

STATS_CHANGED

Change-Id: I55effb0a32ee409649d52a2aa36628d605ac4ed6
diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index 6e950ab..117e5d0 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -490,8 +490,7 @@
     sf->tpl_sf.subpel_force_stop = QUARTER_PEL;
 
     sf->tx_sf.adaptive_txb_search_level = boosted ? 2 : 3;
-    sf->tx_sf.tx_type_search.use_skip_flag_prediction =
-        allow_screen_content_tools ? 1 : 2;
+    sf->tx_sf.tx_type_search.use_skip_flag_prediction = 2;
 
     // TODO(any): Refactor the code related to following winner mode speed
     // features