core: free tank info table on exit

This is obviously a pure code-hygiene thing. But with the new
dynamic tank info table, this becomes trivial, so let's do it.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

subsurface-mobile-main.cpp

@@ -86,6 +86,7 @@ int main(int argc, char **argv)
 	qPref::sync();
 
 	free_prefs();
+	clear_tank_info_table(&tank_info_table);
 	return 0;
 }