CLEANUP: h2: Remove unused labels from mux_h2.c

This removes the unused next_header_block and try_again labels
from mux_h2.c.

try_again is unused as of a76e4c21839cafd036fbe755416569206502c1d9,
which first appeared in haproxy 1.8.0.
next_header_block is unused as of 872855998bd03d5224e0e5cd6aef9b91e2a6de1d,
which was backported to haproxy 1.8.0 as
59fcb216085a7aa9744cffe39567c80de4ebd6bf.
diff --git a/src/mux_h2.c b/src/mux_h2.c
index 6c63b86..9b42d7b 100644
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -2913,7 +2913,6 @@
 	 * block does not wrap and we can safely read it this way without
 	 * having to realign the buffer.
 	 */
- next_header_block:
 	ret = h1_headers_to_hdr_list(bo_ptr(buf), bo_ptr(buf) + buf->o,
 	                             list, sizeof(list)/sizeof(list[0]), h1m);
 	if (ret <= 0) {
@@ -2932,7 +2931,6 @@
 
 	chunk_reset(&outbuf);
 
- try_again:
 	while (1) {
 		outbuf.str  = bo_end(h2c->mbuf);
 		outbuf.size = bo_contig_space(h2c->mbuf);