Clean up Stickyfill's created in diff_file_header

Description

The following discussion from !21076 (merged) should be addressed:

• @pslaughter started a discussion:

  issue (non-blocking): It looks like we never remove the sticky polyfill objects that are created. This is somewhat significant since these diff_file_header can show up a lot.

  Let's handle this in a follow up. 😄

Oh yeah? How are we expected to remove these things?

Stickyfill.remove