buildsys: merge old fwlist files

Besides all newer fwlists contained all older ones (besides one execption),
so no real point in keeping them separated.

I propose to always merge the fwlist from all but the current
releases. I.e., keep all fwlists from kernels released during the PVE
5.0 lifetime separated, once we move to PVE 6.0 we merge the older
ones and start again.
merged with:

sort -u fwlist-2* fwlist-3* fwlist-4.2.* fwlist-4.4.* fwlist-4.4-and-older-pve

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>