Revert "grub2: Exit gracefully if the configuration has BLS enabled"

This reverts commit 985a141.

Reverting for now due to some users experiencing no boot entries after
upgrading. See for background:

ostreedev#1929
https://discussion.fedoraproject.org/t/boot-entries-gone-after-upgrade/8026

src/boot/grub2/grub2-15_ostree

@@ -26,13 +26,6 @@ if ! test -d /ostree/repo; then
     exit 0
 fi
 
-# Gracefully exit if the grub2 configuration has BLS enabled,
-# since there is no need to create menu entries in that case.
-. /etc/default/grub
-if test ${GRUB_ENABLE_BLSCFG} = "true"; then
-    exit 0
-fi
-
 # Make sure we're in the right environment
 if ! test -n "${GRUB_DEVICE}"; then
     echo "This script must be run as a child of grub2-mkconfig" 1>&2