CLEANUP: mux-h2: clean the stream error path on HEADERS frame processing

In h2c_frt_handle_headers() and h2c_bck_handle_headers() we have an unused
error path made of the strm_err label, while send_rst is used to emit an
RST upon stream error after forcing the stream to h2_refused_stream. Let's
remove this unused strm_err block now.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index d74d514..59d76b7 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -1927,13 +1927,6 @@
 	h2c_error(h2c, error);
 	goto out;
 
- strm_err:
-	if (h2s) {
-		h2s_error(h2s, error);
-		h2c->st0 = H2_CS_FRAME_E;
-	}
-	else
-		h2c_error(h2c, error);
  out:
 	h2_release_buf(h2c, &rxbuf);
 	return NULL;
@@ -2003,15 +1996,6 @@
  conn_err:
 	h2c_error(h2c, error);
 	return NULL;
-
- strm_err:
-	if (h2s) {
-		h2s_error(h2s, error);
-		h2c->st0 = H2_CS_FRAME_E;
-	}
-	else
-		h2c_error(h2c, error);
-	return NULL;
 }
 
 /* processes a DATA frame. Returns > 0 on success or zero on missing data.