Revert "Add canonical mock for MediaStreamInterface"

This reverts commit e217217bf3782dbd3ea27be33d5ebd26ae0500ca.

Reason for revert: break upstream project (name collision)

Original change's description:
> Add canonical mock for MediaStreamInterface
>
> Needed to let upstream APIs integrate changes more easily.
>
> Bug: webrtc:13980
> Change-Id: I6cd46f75d56597c10e08d0d66e16089516f5129c
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/259821
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Reviewed-by: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#36613}

Bug: webrtc:13980
Change-Id: I18b91327225e0f844af5dd86c9b4ca8d6301d03e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/259860
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36614}