Deprecated remote_create_with_filename for AdImage

Summary:
In an effort to create stronger parity with the PHP SDK, the AdImage object
creates image_hashes using the same method as PHP.

This keeps the SDK's API a little more consistent as the developer doesn't
need to remember alternate create methods.

Before:
image = AdImage(parent_id=...)
image.remote_create_with_filename(filename='./blah.jpg')

After:
image = AdImage(parent_id=...)
image[AdImage.Field.filename] = './blah.jpg'
image.remote_create()

Test Plan: Run test or attempt to create an AdImage using the above code