rtc: Remove const from parameter in function

In function fill_variance_tree_leaves(), const
for is_key_frame is not needed.

Change-Id: Id8cd827333f1cd417dd965f8ba0a0d56d15c9710
(cherry picked from commit c7402b82e168af554eb543b920e69fd1c297a105)
diff --git a/av1/encoder/var_based_part.c b/av1/encoder/var_based_part.c
index 5d808b6..d113fc8 100644
--- a/av1/encoder/var_based_part.c
+++ b/av1/encoder/var_based_part.c
@@ -1014,7 +1014,7 @@
     PART_EVAL_STATUS *force_split, int avg_16x16[][4], int maxvar_16x16[][4],
     int minvar_16x16[][4], int *variance4x4downsample, int64_t *thresholds,
     uint8_t *src, int src_stride, const uint8_t *dst, int dst_stride,
-    const bool is_key_frame) {
+    bool is_key_frame) {
   AV1_COMMON *cm = &cpi->common;
   MACROBLOCKD *xd = &x->e_mbd;
   const int is_small_sb = (cm->seq_params->sb_size == BLOCK_64X64);