Revert "Cleanup current slot logic"

* This should be left for when/if verity is figured out

This reverts commit 6793b22d9b7b839e9b95240e1245d9ad0b82fc10.

build/meta/com/google/android/update-binary

@@ -39,7 +39,11 @@ umount /system || true
 if [ "$SYSTEMASROOT" == "true" ]; then
   CURRENTSLOT=`getprop ro.boot.slot_suffix`
   if [ ! -z "$CURRENTSLOT" ]; then
-    TARGETSYSTEM=/dev/block/bootdevice/by-name/system"$CURRENTSLOT"
+    if [ "$CURRENTSLOT" == "_a" ]; then
+      TARGETSYSTEM=/dev/block/bootdevice/by-name/system_a
+    else
+      TARGETSYSTEM=/dev/block/bootdevice/by-name/system_b
+    fi
   else
     TARGETSYSTEM=/dev/block/bootdevice/by-name/system
   fi