/usr/share/gnome-session/sessions/gnome-flashback-compiz.session is in gnome-session-flashback 3.22.0-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [GNOME Session]
Name=GNOME Flashback (Compiz)
RequiredComponents=gnome-flashback-init;gnome-flashback;gnome-panel;compiz;gnome-settings-daemon;nautilus-classic;
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