Remove any reference to hook_nodeapi()

[avpaderno]

For example, the _nodeapiexample.info contains the following description.

Demonstrates using the hooknode* APIs (formerly hook_nodeapi) to alter a node from a different module.

hook_nodeapi() is a hook that is used until Drupal 6. Drupal 7 does not use it anymore (as it replaced it with the hook_node_*() hooks); Backdrop has never used it. Any reference to hook_nodeapi() is not useful to developers and should be removed.

[avpaderno]

The reference to hook_nodeapi() could be helpful to Drupal 6 developers, but last Drupal 6 release has been created on February 24, 2016. Nowadays, there is probably no developer who uses Drupal 6 or remembers the Drupal 6 API to find that reference helpful.

I would do as Backdrop core does and remove any reference to Drupal 6 and its API.