tar: fix circular dependency on xz

tar: fix circular dependency on xz

tar depended both on xz and xz-utils which xz already depended on.
Coupled with if PACKAGE_tar check it caused all packages that depended
on tar to have a circular Kconfig dependency. Remove the check and
dependency on xz-utils and leave xz one only.

Move libzstd dependency into DEPENDS.

Fixes: ad82c17 ("tar: fix EXTRA_DEPENDS")
Fixes: https://github.com/openwrt/packages/issues/28141
Signed-off-by: George Sapkin <redacted>