Remove cast of functions to (hb_destroy_func_t)

[behdad]

It's undefined to call functions with a different signature. So we need to add wrappers that match hb_destroy_func_t signature and call those.

Originally reported and discussed here:
https://bugs.chromium.org/p/chromium/issues/detail?id=696729

[drott]

Thank you for fixing these.

[drott]

There are two more instances with likely the same root cause in 758478 and 761245, would be great if we could have a fix soon. Thanks very much.