Ly sources non .desktop files in session directories

[wizetek]

Steps to reproduce

1. Create a file /usr/share/xsessions/foo.bar with similar contents:

[Desktop Entry]
Name=foo
Exec=pkill -x ly-dm

2. (Re)start ly.service
3. Note that "foo" now appears in Ly's menu as one of the available sessions

Other desktop managers seem to ignore file names that are not .desktop. This can serve as a convenient mechanism to disable unwanted entries by renaming these files. In Ly's case they need to be removed altogether.