USE-635: Removing hardcoded USE beta banner from homepage

[djanelle-mit]

Developer

To prepare for the USE Launch, we need to remove a hardcoded banner we added to promote the Beta version of USE. This was hardcoded into the homepage, and this work removes the reference to the banner partial, the banner partial itself, and relevant styling from the alerts scss partial.

Stylesheets

• Any theme or plugin whose stylesheets have changed has had its version
  string incremented.

Secrets

• All new secrets have been added to Pantheon tiers
• Relevant secrets have been updated in Github Actions
• All new secrets documented in README

Documentation

• Project documentation has been updated
• No documentation changes are needed

Accessibility

• ANDI or Wave has been run in accordance to
  our guide and
  all issues introduced by these changes have been resolved or opened as new
  issues (link to those issues in the Pull Request details above)

Stakeholder approval

• Stakeholder approval has been confirmed
• Stakeholder approval is not needed

Dependencies

YES | NO dependencies are updated

Code Reviewer

• The commit message is clear and follows our guidelines
  (not just this pull request message)
• The changes have been verified
• The documentation has been updated or is unnecessary
• New dependencies are appropriate or there were no changes