Revert "lib: Manually unmount /boot before board reset"

This reverts commit 8c71fb5c.

Filesystem corruption during image creation has been fixed in
pkg/user-mode-linux

Signed-off-by: Frédéric Danis <frederic.danis@collabora.com>

update-manager-common.sh

@@ -198,11 +198,6 @@ update_manager_phases()
 	case "$PHASE" in
 	"") PHASE="0";;
 	"done")
-		# Workaround: manually unmount the boot partition before the board is
-		# reset by Lava to prevent unexpected entries in /boot/lost+found
-		# which can prevent subsequent boots.
-		# see https://phabricator.apertis.org/T8501
-		systemd-mount --umount /boot
 		exit 0;;
 	failed\ *)
 		echo "Canceled phase because an error occured earlier"
@@ -238,12 +233,6 @@ update_manager_phases()
 
 	trap '' EXIT
 
-	# Workaround: manually unmount the boot partition before the board is
-	# reset by Lava to prevent unexpected entries in /boot/lost+found
-	# which can prevent subsequent boots.
-	# see https://phabricator.apertis.org/T8501
-	systemd-mount --umount /boot
-
 	echo "finished"
 }