Make ZipFileTest#testHugeZipFile faster, and reduce ZipFile memory usage.

This test was timing out because of unbuffered I/O.

ZipFile was creating an unnecessary byte[] when writing out the central
directory. In the case of these tests, that was an extra 3MiB of heap!

(cherry-picked from a57c521b9d250f909508af771b96c0011676a968.)

Bug: 6481730
Change-Id: I923e563421056c9c0e73246357ccf54d8fb60cdb
2 files changed