Fix #2584: No longer check clipboard if ref code exists on launch.

[jhreis]

Summary of Changes

This pull request fixes #2584

No longer allow ref codes to be overwritten from clipboard on subsequent launches when network request fails.

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()

Test Plan:

1. Copy a referral link (or retrieve from website) F83AB73F-9852-4F01-ABA8-7830B8825993:ABC123
2. Disable internet
3. Launch Brave (reads from clipboard)
4. See ref code in settings
5. Force quit Brave
6. Copy new ref code (F83AB73F-9852-4F01-ABA8-7830B8825993:XYZ789)
7. Re-open Brave (internet still off)
8. Look at settings, should still see same / old ref-code
9. Quite Brave
10. Enable internet
11. Re-open Brave
12. Check logs (should see some server response, either invalid code, or a download id)

Screenshots:

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • release-notes/(include|exclude)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue is assigned to a milestone (should happen at merge time).