Stop offering Steam games as applications

Steam writes a desktop entry for every game somebody asks for a shortcut
to, and it starts the same program the client's own entry does:

    Exec=steam steam://rungameid/3527290

The scan only ever looked at the first token, found steam there, and filed
the game under the same kind as the client. So PEAK sat in the applications
list reading "on (Steam)", counted towards the applications covered, and
offered a space bar to switch it off again - as though it were something
this program had anything to offer. It is not: a game is whatever engine it
was built with, and none of them reads a Chromium argument.

An entry carrying a steam:// address of its own is not a program, it is one
more way of starting Steam. The client's own entry never has one - it takes
an address from the outside, through %U - and that is what tells the two
apart. Those entries go to the Steam module now instead of into the list.

They keep -noverifyfiles, for the same reason the rest of the Steam handling
has it: starting a game with the client closed is a Steam start like any
other, and without the switch it finds the patched web helper script, puts
its own copy back, and the interface loses autoscroll for the rest of the
session.

README.md

@@ -125,6 +125,12 @@ as soon as it is set to run at login: that one bypasses the menu entry entirely,
 and without the switch a Steam started at login finds the patched script,
 restores it, gets patched again, and never gets past its update dialog.
 
+The shortcuts Steam writes for single games get the switch as well. A game is
+not an application this program has anything to offer — none of them is a
+Chromium process and none appears in the applications list — but starting one
+with Steam closed is a Steam start like any other, and leaving the switch out
+there costs the interface its autoscroll for the rest of the session.
+
 **The trade-off is real**: with verification off, Steam no longer repairs a
 damaged installation by itself. That is why Steam is a switch of its own rather
 than part of the general handling — turn it off in the settings and Steam is