Drop remnants of rake package:apple support

The `package:apple` rake task was used to install a version of CFPropertyList
to speed up plist reads/writes. However, that task has been broken since at
least commit d988fe7 when the file_mapping.yaml
file was deleted:

    bundle exec rake package:apple
    rake aborted!
    Could not load Apple file mappings from 'ext/osx/file_mapping.yaml'

Since the `package:apple` rake task hasn't worked since 2021, delete the
cfproperty rake task and the "pre_tasks" entry that registers the cfpropertylist
task with the packaging gem.

Author: joshcooper

ext/project_data.yaml

@@ -6,5 +6,3 @@ gem_rdoc_options:
   - --main
   - README.md
   - --line-numbers
-pre_tasks:
-  'package:apple': 'cfpropertylist'