Revert "[glib/ucdn/icu/ft/ot] Make returned funcs inert"

This reverts commit 5daf3bd4494cce6b4fb074533be9e99c4d9e0edd.

If other atexit callbacks try to destruct the objects we destruct
in atexit callbacks, bad things will happen.

I'll come up with some other way to catch premature destruction
of HB-owned objects.

Fixes https://github.com/behdad/harfbuzz/issues/618
6 files changed