LU-12561 kernel: Remove RHEL6 series and targets

LU-12561 kernel: Remove RHEL6 series and targets

Remove the RHEL6 series and target files.

Also remove the RHEL5 (wow!) targets, and the outdated
Fedora (fc) targets.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I00fc47cac656bc3b6f220f3994f0a25ed73879f9
Reviewed-on: https://review.whamcloud.com/35545
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>