slightly clean up CircleCI config (#2325)
slightly clean up CircleCI config (#2325)

- We only need one branch of googleapis
- There's no need to "install" toolkit; we only need the jar.
googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator,googleapis/gapic-generator