Disable extensive joint motion search at speed 3

Speed/quality tradeoff was good.
Borg test result:
Speed 3
         avg_psnr:  ovr_psnr:  ssim:  speedup:
lowres2:  0.036      0.023     0.067   3.0%
midres2:  0.051      0.052     0.010   4.1%
hdres2:   0.073      0.073     0.044   5.6%

Speed 4
         avg_psnr:  ovr_psnr:  ssim:  speedup:
lowres2:  0.010      0.009     0.039   3.7%
midres2:  0.068      0.063     0.070   5.0%
hdres2:   0.033      0.041     0.042   7.2%

STATS_CHANGED

Change-Id: Iced40538bdb2bdde532cf9f032033b7d709fe886
diff --git a/av1/encoder/speed_features.c b/av1/encoder/speed_features.c
index fe5649e..450596c 100644
--- a/av1/encoder/speed_features.c
+++ b/av1/encoder/speed_features.c
@@ -534,6 +534,7 @@
     // The values in x->pred_mv[] differ for single and multi-thread cases.
     // See aomedia:1778.
     // sf->mv_sf.adaptive_motion_search = 1;
+    sf->mv_sf.disable_extensive_joint_motion_search = 1;
     sf->mv_sf.full_pixel_search_level = 1;
     sf->mv_sf.simple_motion_subpel_force_stop = QUARTER_PEL;
     sf->mv_sf.subpel_search_method = SUBPEL_TREE_PRUNED;
@@ -681,7 +682,6 @@
         frame_is_intra_only(&cpi->common) ? 0 : 1;
     sf->lpf_sf.disable_lr_filter = 1;
 
-    sf->mv_sf.disable_extensive_joint_motion_search = 1;
     sf->mv_sf.prune_mesh_search = 1;
 
     sf->tpl_sf.prune_starting_mv = 3;