Refactor common strings out of EligibilityVerifier

[thekaveman]

With the Veteran's work and copy updates, we've gone back to a single "Unverified" page design and copy, meaning we don't need per-flow copy changes like EligibilityVerifier.unverified_title and EligibilityVerifier.unverified_blurb.

In an effort to simplify our page building (see also #1442), let's move these common fields out of our models and into the page templates directly.

Acceptance Criteria

• unverified_title and unverified_blob fields are removed from the EligibilityVerifier model
• the unverified.html template directly renders the necessary (translated) content.

Additional context