Revert "compress each firmware file with ZSTD"

Revert "compress each firmware file with ZSTD"

While the kernel supports it well, the initramfs-tools lack support
for finding those files when assembling the initrd.

While ubuntu has already support, and the changes required seem not
all to bad (just a simple shell script checking if a path exists),
lets avoid patching and packaging a new initramfs-tools and rather
revert this for now..

This reverts commit 1885bf2becfe373b1988e0efb974a1b090f38dbb.

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