canvas-media trying to use constants defined in canvas-rce doesn't work
because that dependency is not declared.

We don't want to declare it because that would create a cycle.

flag=none

Test Plan:
(From the original PS that introduced these constants)
- Verify the latest RCS is pulled and running
- Start notorious
- Attempt to upload a CC file for a video
  that exceeds 295kb
- Verify that an error message is shown indicating
  the file size is too large
- Verify that you can still upload CC files < 295 kb
- Upload a another video. In the upload modal, choose
  the option to also add captions.
- Attempt to add a caption file > 295 kb and upload
  the video
- Verify a file size error is shown
- Verify you can upload captions for a video in the
  upload modal if the caption file size < 295 kb

Change-Id: Iad11968614dd9b33d9ae40723d1f104e45215f5e
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/298909
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Ed Schiebel <eschiebel@instructure.com>
Product-Review: Jon Scheiding <jon.scheiding@instructure.com>
Reviewed-by: Ed Schiebel <eschiebel@instructure.com>