nixos/stage1: run fsck on battery too

We are in 2021 almost 2022 not in 2004 when this may have been an issue!

https://alioth-lists.debian.net/pipermail/pkg-sysvinit-devel/2009-May/003196.html
https://www.nico.schottelius.org/blog/debian-ubuntu-fsck-skip-on-battery-bug/
https://github.com/OpenRC/openrc/commit/d29daf395299fc97b8e13676bc282800a8bddae8
https://bugs.launchpad.net/ubuntu/+source/laptop-mode/+bug/11194

nixos/modules/system/boot/stage-1-init.sh

@@ -263,15 +263,6 @@ if test -n "$debug1devices"; then fail; fi
 @postDeviceCommands@
 
 
-# Return true if the machine is on AC power, or if we can't determine
-# whether it's on AC power.
-onACPower() {
-    ! test -d "/proc/acpi/battery" ||
-    ! ls /proc/acpi/battery/BAT[0-9]* > /dev/null 2>&1 ||
-    ! cat /proc/acpi/battery/BAT*/state | grep "^charging state" | grep -q "discharg"
-}
-
-
 # Check the specified file system, if appropriate.
 checkFS() {
     local device="$1"
@@ -316,13 +307,6 @@ checkFS() {
         return 0
     fi
 
-    # Don't run `fsck' if the machine is on battery power.  !!! Is
-    # this a good idea?
-    if ! onACPower; then
-        echo "on battery power, so no \`fsck' will be performed on \`$device'"
-        return 0
-    fi
-
     echo "checking $device..."
 
     fsckFlags=