MINOR: buffer: remove bi_end()

It was replaced by ci_tail() when the channel is known, or b_tail() in
other cases.
diff --git a/src/flt_http_comp.c b/src/flt_http_comp.c
index d80dc08..0ccf23b 100644
--- a/src/flt_http_comp.c
+++ b/src/flt_http_comp.c
@@ -207,9 +207,9 @@
 
 		c_adv(chn, *nxt);
 		block = ci_contig_data(chn);
-		memcpy(bi_end(tmpbuf), ci_head(chn), block);
+		memcpy(b_tail(tmpbuf), ci_head(chn), block);
 		if (len > block)
-			memcpy(bi_end(tmpbuf)+block, buf->data, len-block);
+			memcpy(b_tail(tmpbuf)+block, buf->data, len-block);
 		c_rew(chn, *nxt);
 
 		tmpbuf->i += len;