ipc: a modifier keysym is no key

Shift, Control, and their kin were mapped to special keys that the
engine then had a range and a check to ignore, and the GTK module made a
round trip to the daemon for each press.  ipckeysym maps them to key 0,
which was already the "no key" every frontend and the engine skip;
Kmodfirst, Kmodlast, and ismodkey go.

ipc.h

@@ -45,8 +45,6 @@ enum
 	Khenkan = Kspec|0x23,
 	Kkana = Kspec|0x27,
 	Kzenkaku = Kspec|0x2a,
-	Kmodfirst = Kspec|0xe1,
-	Kmodlast = Kspec|0xee,
 
 	/* X core modifier bits; GDK and IBus also flag Super at bit 26. */
 	Mshift = 1<<0,