package kit: Actually add support for B_HPKG_COMPRESSION_NONE

Until now we always declared in the HPKG header that the package file is
zlib compressed. For uncompressed files we would just store all
individual chunks uncompressed. Now we handle completely uncompressed
files slightly differently: We don't write the redundant chunk size
table anymore. The size savings are minor, but it makes the uncompressed
format read-streamable which may be handy.
package: Explicitly use B_HPKG_COMPRESSION_NONE