Clean up some

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• are either individually buildable or squashed
• have commit messages which describe what they do (referring to [Notes][notes] and tickets using #NNNN syntax when appropriate)
• Motivations: In the GHC codebase now:
  • We reinvent some functions of "base" many times (for example: fmap).
  • We have a few little-used (or, in some cases, not used at all!) utility functions with very small definitions (for example: some are merely fmap . fmap). (If a utility function is widely used, i left it alone.)
  • We miss opportunities to derive instances.

I checked the perf metrics locally and saw no major differences.

If you would like me to split up this MR, please let me know! I thought splitting it too far might actually increase burden on reviewers, but maybe that's not true.