MINOR: htx: Move the macro IS_HTX_STRM() in proto/stream.h

The macro IS_HTX_STRM() only relies on stream flags. So move it in
proto/stream.h.
diff --git a/include/proto/proto_http.h b/include/proto/proto_http.h
index 2f8be3f..102c5de 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -29,8 +29,6 @@
 #include <proto/channel.h>
 #include <proto/stream.h>
 
-#define IS_HTX_STRM(strm) ((strm)->flags & SF_HTX)
-
 extern struct pool_head *pool_head_uniqueid;
 
 int process_cli(struct stream *s);
diff --git a/include/proto/stream.h b/include/proto/stream.h
index 1461554..60338c9 100644
--- a/include/proto/stream.h
+++ b/include/proto/stream.h
@@ -31,6 +31,8 @@
 #include <proto/stick_table.h>
 #include <proto/task.h>
 
+#define IS_HTX_STRM(strm) ((strm)->flags & SF_HTX)
+
 extern struct pool_head *pool_head_stream;
 extern struct list streams;