Remove an outdated assertion

The check condtion on block size is deprecated. No need to keep
this assertion around.

Change-Id: Icf2dde2a678cbbce837798877634b7be54e86e67
diff --git a/av1/encoder/rdopt.c b/av1/encoder/rdopt.c
index f542ce1..f01a31a 100644
--- a/av1/encoder/rdopt.c
+++ b/av1/encoder/rdopt.c
@@ -1489,7 +1489,6 @@
 #endif  // CONFIG_RECT_TX
   int ext_tx_set;
 #endif  // CONFIG_EXT_TX
-  assert(bs >= BLOCK_8X8);
 
   if (tx_select) {
 #if CONFIG_EXT_TX && CONFIG_RECT_TX