Revert "Revert "[ruby/fiddle] Use ffi_closure_free by default. (#20)""

This reverts commit efd641ffab34e433a8d8a7d78914576f2425aa90.

This changeset seems to be needed to suppress a warning on Ubuntu 20.04
https://rubyci.org/logs/rubyci.s3.amazonaws.com/ubuntu/ruby-master/log/20200304T033004Z.log.html.gz
```
closure.c:264:5: warning: 'ffi_prep_closure' is deprecated: use ffi_prep_closure_loc instead [-Wdeprecated-declarations]
  264 |     result = ffi_prep_closure(pcl, cif, callback, (void *)self);
      |     ^~~~~~
```

I guess there was a reason why the commit was reverted (maybe some CIs
failed?), so try it again.

0 files changed, 0 insertions, 0 deletions