Delete the custom variables related to content types if they really exists

Problem/Motivation

If you uninstall the module the following code is executed:

  foreach (array_keys(node_type_get_names()) as $type) {
    variable_del('node_revision_delete_track_' . $type);
    variable_del('node_revision_delete_number_' . $type);
  }

You have a loop over all your content types and you execute for each content type twice the variable_del() function, even if the variables doesn't exists.

Proposed resolution

Search the existing module variables related to content_types and then delete them all.

Remaining tasks

Write the code.

User interface changes

None.

API changes

None.

Data model changes

None.