Drop not injectable fields before single linkfield workaround

[cconard96]

Since glpi-project/glpi#8816, there was a second search option with the same "users_id" link field. Then in the workaround for #121, the correct User option gets removed and the Appliance User option remains. This remaining option isn't injectable though and is dropped later anyways. It makes sense to drop all non-injectable options before the workaround.

fixes #259
fixes #243
fixes #233

[cconard96]

Last commit addresses issue where the plugin tried searching for the entities_id search option which isn't injectable and is now not present in the results but is statically set internally.