Rename write_bitdepth_colorspace_sampling.

Rename write_bitdepth_colorspace_sampling to write_color_config to match
the renaming of the corresponding av1_read_bitdepth_colorspace_sampling
on the decoder side in commit a19fdce62ef2a52bb7e2b9b34d84506c378c0122.

BUG=aomedia:1899

Change-Id: I05c1ba99243e6c549c4a4a80ebc757f433c8767a

av1/encoder/bitstream.c

diff --git a/av1/encoder/bitstream.c b/av1/encoder/bitstream.c
index 9db6a42..02785f3 100644
--- a/av1/encoder/bitstream.c
+++ b/av1/encoder/bitstream.c
@@ -2452,8 +2452,8 @@
   }
 }
 
-static void write_bitdepth_colorspace_sampling(
-    AV1_COMMON *const cm, struct aom_write_bit_buffer *wb) {
+static void write_color_config(AV1_COMMON *const cm,
+                               struct aom_write_bit_buffer *wb) {
   write_bitdepth(cm, wb);
   const int is_monochrome = cm->seq_params.monochrome;
   // monochrome bit
@@ -3599,8 +3599,7 @@
   }
   write_sequence_header(cpi, &wb);
 
-  // color_config
-  write_bitdepth_colorspace_sampling(cm, &wb);
+  write_color_config(cm, &wb);
 
 #if !CONFIG_BUFFER_MODEL
   // timing_info