bootrc: remove usbwait hack, usbd/nusbrc are now synchronous by previous commit

sys/man/8/plan9.ini

@@ -837,9 +837,6 @@ The main feature of the interface is the ability to watch
 battery life (see
 .IR stats (8)).
 It is not on by default because it causes problems on some laptops.
-.SS \fLusbwait=\fIvalue\fP
-This changes the sleep time from the default 2 to value in cases of
-USB devices taking a long time to come online.
 .SS \fLnousbhname=\fP
 When defined,
 .IR nusbrc (8)

sys/src/9/boot/bootrc

@@ -175,12 +175,6 @@ if(test -x /bin/aux/kbdfs){
 if(test -x /bin/nusbrc && ! test -e /env/nousbrc)
 	nusbrc
 
-# wait for devices to settle down
-if(~ $#usbwait 1)
-	sleep $usbwait
-if(~ $#usbwait 0)
-	sleep 2
-
 # load boot methods
 fn showlocaldevs {}
 fn configlocal {}