Remove not used image (#3139)

Summary:
This image was moved to `test/assets/encode_jpeg` in #2988 but was not removed in this branch for some reason

Pull Request resolved: #3139

Reviewed By: datumbox

Differential Revision: D25395596

Pulled By: fmassa

fbshipit-source-id: a0afdec2d1da41e6743d7d723e71ffde442cf3a7

Author: fmassa