refactor(tile-manifest): delete dead convertV1ToV2 function and its tests
The v1 manifest format is gone — convertV1ToV2 had no live callers,
only its own unit tests. Removed the function from tile-manifest.ts
and the corresponding describe('convertV1ToV2') block plus the import
from tile-manifest.test.ts. VALID_V1_MANIFEST stays — still used by
detectManifestVersion and parseManifestJSON tests.