VACMS-14955: Hide ief_reference_save button for CLP

[Becapa]

Description

Relates to #14955.

QA steps

As a user with access to create Campaign Landing Pages

1. Add a new Campaign Landing Page (/node/add/campaign_landing_page)
2. Scroll down to 'Downloadable Resources' and open the section.
3. Click to 'Enable this page segment'
4. Under the 'Resources' section click the 'Add existing Downloadable resource'

• Verify that there are now only 2 buttons: 'Select Downloadable resource' and 'Cancel'

5. Click to 'Select Downloadable resource' and choose a file in the modal that pops up.

• Verify that you can select a resource and it then shows up in the table.

6. Click to 'Add existing Downloadable resource' again.
7. Click to 'Select Downloadable resource' and choose another file.

• Verify that a second file is added to the table.

Definition of Done

• Documentation has been updated, if applicable.
• Tests have been added if necessary.
• Automated tests have passed.
• Code Quality Tests have passed.
• Acceptance Criteria in related issue are met.
• Manual Code Review Approved.
• If there are field changes, front end output has been thoroughly checked.

Select Team for PR review

• CMS Team
• Public websites
• Facilities
• User support
• Accelerated Publishing

Is this PR blocked by another PR?

• DO NOT MERGE

Does this PR need review from a Product Owner

• Needs PO review

CMS user-facing announcement

Is an announcement needed to let editors know of this change?

• Yes, and it's written in issue ____ and queued for publication.
  • Merge and ping the UX writer so they are ready to publish after deployment
• Yes, but it hasn't yet been written
  • Don't merge yet -- ping the UX writer to write and queue content
• No announcement is needed for this code change.
  • Merge & carry on unburdened by announcements

[Becapa]

LGTM!