Fix extra subitem arrows

[phudson-he]

Types of changes

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Description of Change

When accessibility mode is on, and any left nav item that has subitems, extra arrows are displayed.

Issues Solved

Closes #11031

Checklist

• I targeted one of these branches:
  • [ ] dev/7.6.x (under development): features, bugfixes not covered below
  • [x] dev/7.5.x (main support): regressions, crashing bugs, security issues, major bugs in new features
  • [ ] dev/6.2.x (extended support): major security issues, data loss issues
• [ ] I added a changelog in arches/releases
• [ ] I submitted a PR to arches-docs (if appropriate)
• [ ] Unit tests pass locally with my changes
• [ ] I added tests that prove my fix is effective or that my feature works
• [ ] My test fails on the target branch

Ticket Background

• Sponsored by: Historic England
• Found by: @phudson-he
• Tested by: @phudson-he
• Designed by: @phudson-he