Remove the remaining optional layout_builder_iframe_modal.settings config

Problem/Motivation

Hi
Whatever configuration i change anywhere locally when i try to import it with my gitlab-ci deployment it always fail and send me the below message

// Import the listed configuration changes?: yes.                              
 [error]  Drupal\Core\Config\ConfigImporterException: There were errors validating the config synchronization.
Configuration <em class="placeholder">layout_builder_iframe_modal.settings</em> depends on the <em class="placeholder">layout_builder_iframe_modal</em> extension that will not be installed after import. in Drupal\Core\Config\ConfigImporter->validate() (line 794 of /home/braiezkg/varbdev/docroot/core/lib/Drupal/Core/Config/ConfigImporter.php). 
In ConfigImportCommands.php line 324:
                                                                               
  The import failed due to the following reasons:                              
  Configuration <em class="placeholder">layout_builder_iframe_modal.settings<  
  /em> depends on the <em class="placeholder">layout_builder_iframe_modal</em  
  > extension that will not be installed after import.                         

I even make sure that databases (local & prod) are the same by exporting local db to the replace the one online.Immediate drush cim on production will confirm that no changes has been made. But as soon as i change any configuration, export it and try to import online the error is back

Steps to reproduce

• on local site change any configuration
• drush cex
• Move to production site
• drush updb
• drush cim

Proposed resolution

• Remove the leftover optional layout_builder_iframe_modal.settings config if the module was uninstalled.
• Install Layout Builder Modal module if it was not enabled.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ Accessibility and Readability
• ✅ Code review from 1 Varbase core team member
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes and Update Helper on new feature change/addition
• ✅ Release varbase-9.0.15, varbase_layout_builder-10.0.32, Varbase 10.0.0-beta1, varbase_layout_builder-10.1.0-alpha10

Varbase update type

• ✅ No Update
• ➖ Optional Update
• ➖ Forced Update
• ➖ Forced Update if Unchanged

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• Issue #3383937 by delacosta456: Removed the remaining optional layout_builder_iframe_modal.settings config