Prune ab partition for screen contents

Enabled prune_ab_partition_using_split_info feature for screen
contents at speed 4. The average quality & speed changes for
screen contents are given below.

avg_psnr  ovr_psnr  ssim   speedup %
 0.136     0.137    0.132    2.3
Speedup range: 0.8% to 3.7%.

BUG=aomedia:2711

STATS_CHANGED

Change-Id: Icc8b78420e1c39e27a476fd5c945943d0355db1a

av1/encoder/speed_features.c

diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index 36b8518..7d2f666 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -525,8 +525,7 @@
     sf->mv_sf.subpel_search_method = SUBPEL_TREE_PRUNED_MORE;
 
     sf->part_sf.simple_motion_search_prune_agg = 2;
-    sf->part_sf.prune_ab_partition_using_split_info =
-        !allow_screen_content_tools;
+    sf->part_sf.prune_ab_partition_using_split_info = 1;
 
     sf->inter_sf.adaptive_mode_search = 1;
     sf->inter_sf.alt_ref_search_fp = 1;