Show file type and file size accepted in the hint text

# File upload QA v2

Severe:
- If there is a custom file type associated to the form element, you will only know by realizing you can't find it on your device.
- Theres an opportunity to remove the input field in the More modal, and replace the hint text with the file type selection
- Even if there is no file type customization, we could still have a default description of the file types accepted at this time (no mp4 tehe)
- Related to card #5768

Testing:
- Tablet, Edge, EN

Start by locating the file-upload form element and its More modal in the platform-forms-client frontend. Review how custom and default accepted file types are determined, then update the hint to show the accepted file type and file size while removing the redundant input if appropriate. Verify the result on tablet Edge in English, including the no-mp4 case.

Written by the indexing model from the issue text.