Drop GRUB Legacy support and remove its code in ReaR

[jsmeix]

I wonder if GRUB Legacy support in ReaR
is still used anywhere?

For example regarding SUSE and openSUSE:
The SUSE SLES12 release notes
https://www.suse.com/releasenotes/x86_64/SUSE-SLES/12/index.html
read (excerpts):

Publication date: 2016-04-06
...
8.4.8.9 GRUB2 Is the Supported Bootloader
GRUB2 is now available
on all SUSE Linux Enterprise 12 architectures
and is the only supported bootloader.
Other bootloaders that were supported in SLE 11, have been
removed from the distribution and are not available anymore.

So since SLES12 (since October 2014)
GRUB Legacy support is no longer needed in ReaR for SUSE,
cf.
https://en.wikipedia.org/wiki/SUSE_Linux_Enterprise

SUSE Linux Enterprise Server 12 (SLES 12)
... was released on October 27, 2014

This issue is triggered by
#3123 (comment)

[pcahyna]

RHEL 6 uses GRUB legacy. So this would mean dropping support for RHEL 6.

[pcahyna]

By the way @jsmeix , can we remove suport for ELILO as well? I believe it is there because of SLES.

[jsmeix]

@pcahyna regarding ELILO:

In contrast to the GRUB Legacy RPM package 'grub'
that is no longer there in SUSE's internal build service
since SLES12 ('grub' existed up to SLES11)
the ELILO RPM package 'elilo'
is still there in SUSE's internal build service
even up to current SLES15.

I don't know under what circumstances ELILO
might be used by SLES customers with SLES12 or SLES15.
I will try to investigate that but likely this will take time
so I would prefer to let this issue only deal with GRUB Legacy
and deal with ELILO in the separated issue
#3132

[pcahyna]

@jsmeix thanks for the confirmation. It is not a priority, it's just that I saw ELILO when investigating the current bootloader support (that I am about to revamp a bit) so I wanted to avoid having to touch something that would be useless anyway. Since elilo is there, I will count on it in my plans.

[pcahyna]

#3123 (comment) says though:

GRUB2 is now available
on all SUSE Linux Enterprise 12 architectures
and is the only supported bootloader.
Other bootloaders that were supported in SLE 11, have been
removed from the distribution and are not available anymore.

[jsmeix]

Yes, and that contradiction in SLES12 that
"GRUB2 is the only supported bootloader"
but an 'elilo' RPM package still exists
(in SUSE's internal build service)
needs to be investigated by me.

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