Unlisted Packages' pages erroneously show notice that a prerelease version is available

[claycompton]

This is a regression from production. The problem currently occurs in QA.

1. Sign in to qa.nugettest.org and upload a new package.
2. Unlist the package you just uploaded.
3. View the package page for the package.

Result: You'll see an erroneous notice that there's a newer pre-release version available. See attached screenshot.

Expected: We should reserve this for occasions where there's, you know, an actual pre-release version that happens to be newer.