NavigationMojoResponse: Remove the old code path [2/4]

Removes usages of the stream for loading the main resource response
in the renderer process.

Other CLs:
  1) https://chromium-review.googlesource.com/c/chromium/src/+/1015005
* 2) https://chromium-review.googlesource.com/c/chromium/src/+/1021631
  3) https://chromium-review.googlesource.com/c/chromium/src/+/1022790
  4) https://chromium-review.googlesource.com/c/chromium/src/+/1024038

Bug: 705744
Change-Id: I2fa52775d24f12d16c71f615f0c9d7618d1edb1e
Reviewed-on: https://chromium-review.googlesource.com/1021631
Commit-Queue: Arthur Sonzogni <[email protected]>
Reviewed-by: Nasko Oskov <[email protected]>
Cr-Commit-Position: refs/heads/master@{#553172}
23 files changed