depends: qt: avoid system harfbuzz and bz2

Summary:

We may eventually want to break out harfbuzz and build it in depends,
but for now just ensure that runtime dependencies don't depend on
whether or not harfbuzz was present on the builder.

Backport of core PR14385
https://github.com/bitcoin/bitcoin/pull/14385/files

Test Plan: Regenerate the depends and run the gitian builds.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D4099