Revert "copy-firmware: Support additional compressor options"

Revert "copy-firmware: Support additional compressor options"

This reverts commit 2bad80e7edd3c0f84718545d9338c8edfed16513.

The commit effectively added accidental command injection, while it was aiming
to control the compression flags.

In practise you'd want to use ZSTD_CLEVEL and ZSTD_NBTHREADS for zstd. As
documented in zstd(1) it allows for up-to level 19, which is fine since the
kernel does not support higher levels.

Arch, Alpine and likely other distributions have been using this approach
since day one.

The other compressors like xz have equivalent.

Cc: Juerg Haefliger <juerg.haefliger@canonical.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>