Remove unused submodule from gumbo-parser submodule.

diff --git a/thirdparty/gumbo-parser b/thirdparty/gumbo-parser
index 3973c58d759574f2899528d2b3379e17d66dbcad..289f3de61d9fc6a9812a6900c23e74c4d1fbde7d 160000 (submodule)
--- a/thirdparty/gumbo-parser
+++ b/thirdparty/gumbo-parser
@@ -1 +1 @@
-Subproject commit 3973c58d759574f2899528d2b3379e17d66dbcad
+Subproject commit 289f3de61d9fc6a9812a6900c23e74c4d1fbde7d