Currently we have dev dependencies on package:grinder and package:github. Neither are in or are likely to be added to DEPS.

AIs:

• remove grinder dep
  • remove grinder.dart dart-archive/linter#4413
• find a home for github-dependent tool code
  • rationalize tool directory contents #59171
    • remove stale tool code #59172
    • isolate package:github dependent code (and identify a new home) #59173