FIX / Add plugin configuration deletion during desinstallation

[Mary-Clb]

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• The plugin uninstallation function was missing the deletion of glpi_configs entries belonging to the plugin.