flatpak: Remove intltool module

GNOME Calendar itself stopped depending on intltool in 3.25.3. After
intltool got removed from org.gnome.Sdk, it was added to our manifest
in 2019, because EDS still depended on it.

EDS stopped depending on intltool in 2021 (see linked MR).

Since this was the only module we used from the `shared-modules`
project, I also removed that git submodule.

See: <https://gitlab.gnome.org/GNOME/evolution-data-server/-/merge_requests/78>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/802>

.gitmodules

@@ -1,3 +0,0 @@
-[submodule "build-aux/shared-modules"]
-	path = build-aux/shared-modules
-	url = https://github.com/flathub/shared-modules

build-aux/org.gnome.Calendar.json

@@ -116,7 +116,6 @@
                 }
             ]
         },
-        "shared-modules/intltool/intltool-0.51.json",
         {
             "name" : "evolution-data-server",
             "cleanup": [ "/share/GConf" ],