Remove deprecated import values from tests, docs (#1291)

We *long* ago deprecated and renamed some fields in versions and from the versions import code, but still had some lingering references in the docs, tests, and seed data. This removes them from those places (they are still supported but deprecated in the import code). Ultimately, I don't think we've *used* these (except in the seed data) for years, so I'd also like to stop supporting them as deprecated in the importer, but that's needs to be a separate, later step.

Author: Mr0grog

app/assets/data/swagger.yaml

@@ -1187,7 +1187,7 @@ paths:
           default: true
           required: false
           description: >-
-            If set to false, the importer will not create new page records. If the POSTed data contains a version with a `page_url` field that doesn’t match an known page, the version will be skipped and not imported at all.
+            If set to false, the importer will not create new page records. If the POSTed data contains a version with a `url` field that doesn’t match an known page, the version will be skipped and not imported at all.
         - name: skip_unchanged_versions
           in: query
           description: >-
@@ -2147,7 +2147,7 @@ definitions:
   ImportableVersion:
     type: object
     properties:
-      page_url:
+      url:
         type: string
         format: uri
         description: The original URL the version was captured from.