Remove disallowed generic PropTypes workarounds

[arbrandes]

On the Course Import page we're forcing the use of generic object PropType via an ugly PropTypes.objectOf(PropTypes.object). See here:

https://github.com/openedx/frontend-app-library-authoring/blob/f62d0aa/src/library-authoring/course-import/CourseImportPage.jsx#L151

Remove that and alter the ongoingImport data structure accordingly so we can use a definite PropType.

[jristau1984]

This has been brought into the 2U Library Authoring epic with this internal ticket: https://2u-internal.atlassian.net/browse/TNL-10592

[navinkarkera]

@jristau1984 @arbrandes Is this issue still relevant?

[arbrandes]

Yes, the hack is still there:

https://github.com/openedx/frontend-app-library-authoring/blob/f62d0aa/src/library-authoring/course-import/CourseImportPage.jsx#L151

[kdmccormick]

Closing per #439