package: Do not bother with deflating big jpeg images

It takes a lot of time and we can save 1% of size if at all. Rather
store them uncompressed in the zip file.
Maybe we should not deflate jpeg files at all. For some small ones,
about 100KB - 200KB, I've seen 2% savings.
With png, we can save a bit more, although it's still only about 4% - 8%.

Change-Id: I43a3e3812882e4ce85e7af9d0aaab454d98c4860