[native] Remove sortBy property from fetchPhotos

Summary:
Relevant Linear issue here. I left detailed research for this diff in my comment there. This diff sorts out issues with MediaGalleryKeyboard displaying images in a weird order (no pun intended) and instead mirrors the "default sorting provided by the platform" (from the Expo docs).

In summary, photos are now displayed in the same order as on a user's Camera Roll.

Test Plan: Tested on physical iOS device and Android simulator and works as expected. One notable thing I tested was setting the creationTime of a photo to the future and making sure that it wasn't pushed to the front of the photos displayed on MediaGalleryKeyboard. This was the main bug with using creationTime.

Reviewers: atul, tomek

Subscribers: ashoat, adrian

Differential Revision: https://phab.comm.dev/D4836