R1:e1d6bad864d4

Stop trying to assess the image dimensions of large files and file chunks

Summary:
Depends on D18828. Ref T7789. See <https://discourse.phabricator-community.org/t/git-lfs-fails-with-large-images/584>.

Currently, when you upload a large (>4MB) image, we may try to assess the dimensions for the image and for each individual chunk.

At best, this is slow and not useful. At worst, it fatals or consumes a ton of memory and I/O we don't need to be using.

Instead:

- Don't try to assess dimensions for…