We have unnecessary runs of the `test.sh` script. We can simplify the CI
pipeline and at the same time improve the docs build by using `--cfg
docsrs`.
- Remove the `wasm` job, replace it by enabling the `DO_WASM` env var for
the stable toolchain run in the `Tests` job.
- Add `--cfg docrs` flag to the docs build and set the `DO_DOCS` env var
as part of the nightly toolchain run in `Tests` job.
The end result is one less run of the `test.sh` script and better test
coverage.
Tobin Harding
Andrew Poelstra