temporarily removed change_observer

Author: dk949

.gitmodules

@@ -40,6 +40,3 @@
 [submodule "include/add_noexcept/include/ut/add_noexcept"]
 	path = include/add_noexcept/include/ut/add_noexcept
 	url = https://gist.github.com/dk949/d3e0628ee5768bc65c474ec370d77f55
-[submodule "include/change_observer/include/ut/change_observer"]
-	path = include/change_observer/include/ut/change_observer
-	url = https://gist.github.com/dk949/2508ff2b4b5ddf152e7b6c027e8f13c4