Switch back to libusbx master

The hotplug branch in manuelnaranjo's repo has very broken support for
composite devices, blah. So let's switch back to libusbx master and deal
with that.

.gitmodules

 [submodule "server/libusbx"]
 	path = server/libusbx
-	url = https://github.com/manuelnaranjo/libusbx.git
-	branch = windows-hotplug-4
+	url = https://github.com/libusbx/libusbx.git
+	branch = master
\ No newline at end of file