using -Wunused-packages to eliminate unused deps

[hellwolf]

Description

Checklist

• tested locally
• added automated tests
• updated the docs
• updated the changelog

[hellwolf]

• Local build test: cabal build --enable-tests --enable-benchmarks all
• One warning left due to a bug in ghc:

  <no location info>: warning: [GHC-42258] [-Wunused-packages]
      The following packages were specified via -package or -package-id flags,
      but were not needed for compilation:
        - system-cxx-std-lib-1.0 (exposed by flag -package-id system-cxx-std-lib-1.0)
  

[msooseth]

NICE, so much cleaner! Thanks so much!