This PR cleans up some of the documentation post Dawn+Tint merge.
The README is better combined, the building document is moved up
a level as it covers both Tint and Dawn. The various duplicate files
are removed.
Bug: dawn:1339
Change-Id: I829fbc32529a304fbc55eac3fda86d52c1a6952e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/88340
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>