This also removes support for Travis and AppVeyor, as well as git
submodules for dependencies.
It also adjusts .gitignore to include dependencies (submodules are
implicitly ignored but are removed in this commit).
Finally, removes some CMake-specific code from the code generator.
BUG=
Change-Id: I4ebc04e530a574b412ef0ca81e4672db01f0ed92
Reviewed-on: https://dawn-review.googlesource.com/c/2040
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>