index.cgi: Add warning about reiserfs deprecation and removal if reiserfs used

index.cgi: Add warning about reiserfs deprecation and removal if reiserfs used

- Reiserfs was stopped in IPFire in Core Update 167. It has been announced that reiserfs
   will be removed from the kernel in 2025.
- This patch gives a warning about this deprecation and removal if reiserfs is used. The
   warning also requests that the user does a re-installation using either ext4 or xfs
   filesystems.
- Tested out on a vm installation with reiserfs, ext4 and xfs. Messgae shown on system
   with reiserfs filesystem but nopt on the other two.
- Warning message added into the English language file and ./make.sh lang run.

Tested-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>