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.

doc/middleclick-autoscroll.1.scd

@@ -107,6 +107,12 @@ an update dialog. The trade-off is that Steam no longer repairs a damaged
 installation on its own; that is why Steam is a switch of its own in the
 settings.
 
+The shortcuts Steam writes for single games carry the switch too. A game is not
+an application this program has anything to offer and none of them is listed
+under *Applications*, but starting one with Steam closed is a Steam start like
+any other, and without the switch it costs the interface its autoscroll for the
+rest of the session.
+
 Starting Steam some other way - from a terminal, from a script - leaves the
 switch out, and Steam puts its own copy of the script back for that session.
 The patch returns at the next apply with Steam closed. It is deliberately not