classic: Drop separate gnome-session definition
Originally the classic session replaced gnome-shell.desktop
with
gnome-shell-classic.desktop
(to add the --mode=classic parameter)
and added nautilus-classic.desktop
(to force on desktop icons).
Neither is the case anymore (and hasn't been for years): Nowadays the only expected difference is the GNOME_SHELL_SESSION_MODE variable and the DesktopNames field, which are both set from the session .desktop file rather than the gnome-session session definition.
Any difference in the latter - like not starting the USBProtection plugin and missing systemd user session support - are bugs. The easiest way to avoid those in the future is by removing the obsolete duplication that enables them, so do just that.