Remove unneeded check for RESTORE_NONE

Function loop_restoration_write_sb_coeffs() is called only if
av1_loop_restoration_corners_in_sb() returns a nonzero value. This state
only occurs when frame_restoration_type is not RESTORE_NONE, so this
check is unneeded.

Change-Id: I2683f8e34cb33bb562fac67465f2a67cd3f26e7a
diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index bf461dc..2bde02b 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -1907,7 +1907,7 @@
     aom_writer *const w, int plane, FRAME_COUNTS *counts) {
   const RestorationInfo *rsi = cm->rst_info + plane;
   RestorationType frame_rtype = rsi->frame_restoration_type;
-  if (frame_rtype == RESTORE_NONE) return;
+  assert(frame_rtype != RESTORE_NONE);
 
   (void)counts;
   assert(!cm->features.all_lossless);