Remove obsolete note about simple configuration from 'exclude' plugin

Problem/Motivation

The exclude assignment plugin's configuration form includes the following note:

Note that simple configuration will not be excluded as it is always module-provided.

This is no longer accurate. We handle simple configuration just like other configuration. We exclude it if this option is enabled, except from the install profile, which is allowed to override other extension-provided configuration.

Proposed resolution

Remove this obsolete note.

Remaining tasks

User interface changes

API changes

Data model changes