Revert "Temporarily disable simple_bwd_adapt"

This reverts commit c002bdf6987c42f2f60629d88d806ce3fc5fb77d.

Now the issue has been tracked down to what is described in:
https://aomedia-review.googlesource.com/#/c/aom/+/29761/

Change-Id: I49fe8395781e1fea8095dbdc6c00d36b90dc7575
diff --git a/configure b/configure
index a437fa3..961c6fc 100755
--- a/configure
+++ b/configure
@@ -527,6 +527,7 @@
       soft_enable ext_comp_refs
       soft_enable ext_delta_q
       soft_enable parallel_deblocking
+      soft_enable simple_bwd_adapt
       soft_enable loopfilter_level
       soft_enable deblock_13tap
     fi