Ask BazelCI to also download and upload bazel_nojdk builds. (#1025)

* Also build bazel_nojdk for Linux and macOS in the bazel-release pipeline.
* Ask BazelCI to also download and upload bazel_nojdk builds.
* Remove Windows special-casing now that we also build bazel_nojdk.exe.
* Remove another special-casing of Windows.
* Remove yet another Windows special-casing.
* Revert to using "Bazel" as the source_step label.
* Don't download bazel_jdk during execute_commands().
* Minor cleanup.