pkp/pkp-lib#9678 make acron non functional

[touhidurabir]

for pkp/pkp-lib#9678

[jonasraoni]

As the plugin will be fully deprecated, and considering that the issue presents a related and harder breaking change (death of scheduledTasks.xml), I think we can just unlink the submodule (there's basically no public methods to be used by 3rd-parties on this AcronPlugin class) and include a warning on the PKPApplication class:

Hook::addUnsupportedHooks('AcronPlugin::parseCronTab')

Perhaps we can confirm with Alec.

---

Not sure if it's done (I'll review the other PRs yet), but it's needed to update the usage of this hook across the codebase/other plugins that we're maintaining later:
https://github.com/search?q=org%3Apkp+AcronPlugin%3A%3AparseCronTab&type=code

[touhidurabir]

Added the unsupported hook but will removed the submodule reference from .gitsubmodule once we finalise the implementation .