Break end-user dependency on rules_go

[alexeagle]

In rules_typescript we are working to make Bazel work better for a broad user base of Angular developers. One major problem with the first-time user experience is a very large download of the Go SDK.

Our solution is to release rules_typescript with pre-compiled go binaries for each platform. Then the rules_go dependency only appears for us in development, and we strip such load() statements from the starlark code we publish. This should allow our users to drop the rules_go dependency from their WORKSPACE files.

However, rules_typescript depends on rules_webtesting, which still requires the transitive dependency on rules_go. We're happy to help cut this dependency so that Angular developers aren't compiling Go programs from sources.

[alexeagle]

Just discussed in person with @DrMarcII - this seems doable, we'd need to start publishing rules_webtesting releases as github artifacts on e.g. https://github.com/bazelbuild/rules_webtesting/releases/tag/0.2.2
and this published artifact would have to be somewhat transformed to at minimum scrub any load() path from JS user to Go sources.

For reference, we've been making the same change in rules_typescript, eg. bazelbuild/rules_typescript#355