4.15.0-29.31~16.04.1) is not available, but a newer one is (4.15.0-46.49~16.04.1). We redirected you there.
/usr/share/zoneinfo/HST is in tzdata 2016d-0+deb7u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/zoneinfo/posix/HST