Deprecate angle icons in favor of chevrons

Purpose

Now that all known instances of angle icons have been migrated to chevrons, the angles can be removed. See parent epic for more details.

Screenshots

N/A

Checklist

For a new icon and/or illustration:

• Link to related design issue:
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.

Closes #129 (closed)