package/libarchive: remove double handling of zstd

package/libarchive: remove double handling of zstd

When 4bcc34446485d27efd41de70a86355a0e3798838 was applied, it was not
noticed that 96dc6701af877a4aa4da20a9e0d5b849cc5c8356 (from another
contributor) had already been
applied. 4bcc34446485d27efd41de70a86355a0e3798838 essentially did the
same thing as 96dc6701af877a4aa4da20a9e0d5b849cc5c8356, except it also
disable zstd support explicitly in the host-libarchive package.

Let's drop the part of 4bcc34446485d27efd41de70a86355a0e3798838 that
duplicates 96dc6701af877a4aa4da20a9e0d5b849cc5c8356.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>