REORG: include: move common/h2.h to haproxy/h2.h

No change was performed, the file is only included from C files and
currently doesn't need to be split into types+functions.
diff --git a/src/hpack-dec.c b/src/hpack-dec.c
index 8f8e02b..e318ac3 100644
--- a/src/hpack-dec.c
+++ b/src/hpack-dec.c
@@ -35,7 +35,7 @@
 #include <haproxy/hpack-huff.h>
 #include <haproxy/hpack-tbl.h>
 #include <haproxy/chunk.h>
-#include <common/h2.h>
+#include <haproxy/h2.h>
 #include <import/ist.h>
 
 #include <types/global.h>