Simplify bit adaptor for internal ARF

Simplify the rate adaptation for internal ARFs. The compression
performance change is in the range of 0.01%.

STATS_CHANGED

Change-Id: I97f982d15eb53cbf542eb879dd2f0a67223b916a

av1/encoder/ratectrl.c

diff --git a/av1/encoder/ratectrl.c b/av1/encoder/ratectrl.c
index c748f5a..fd82563 100644
--- a/av1/encoder/ratectrl.c
+++ b/av1/encoder/ratectrl.c
@@ -1190,10 +1190,6 @@
   double rate_factor;
 
   rate_factor = rate_factor_deltas[rf_lvl];
-  if (rf_lvl == GF_ARF_LOW) {
-    rate_factor -= (cpi->gf_group.layer_depth[cpi->gf_group.index] - 2) * 0.1;
-    rate_factor = AOMMAX(rate_factor, 1.0);
-  }
   return av1_compute_qdelta_by_rate(&cpi->rc, frame_type, q, rate_factor,
                                     cpi->common.seq_params.bit_depth);
 }