MINOR: channel/buffer: replace b_{adv,rew} with c_{adv,rew}
These ones manipulate the output data count which will be specific to
the channel soon, so prepare the call points to use the channel only.
The b_* functions are now unused and were removed.
diff --git a/src/filters.c b/src/filters.c
index 1bd50c3..26bed64 100644
--- a/src/filters.c
+++ b/src/filters.c
@@ -1089,7 +1089,7 @@
goto end;
/* Consume data that all filters consider as forwarded. */
- b_adv(chn->buf, ret);
+ c_adv(chn, ret);
/* Stop waiting data if the input in closed and no data is pending or if
* the output is closed. */