Close fuchsia-rfc-0153 branch.

Since all development has been moved to the `main`
branch, remove all files from the current branch,
and add a new README.md one explaining the situation
and listing the corresponding `main` commit that
replicates the last known state of this one.

Fixed: 301120237
Change-Id: Ifd3f4ffe22d5d4c547bbcace517e088df6c76f2b
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/github.com/ninja-build/ninja/+/987832
Reviewed-by: Tyler Mandry <tmandry@google.com>
Reviewed-by: David Turner <digit@google.com>