fix: old jhugo book

Author: hugomrdias

.gitmodules

@@ -1,9 +1,6 @@
 [submodule "orient"]
 	path = orient
 	url = https://github.com/filecoin-project/orient.git
-[submodule "hugo/themes/book"]
-	path = hugo/themes/book
-	url = https://github.com/alex-shpak/hugo-book
 [submodule "src/actors"]
 	path = src/actors
 	url = https://github.com/filecoin-project/specs-actors.git