SI-8916 Fix -Ywarn-unused-import warnings
SI-8916 Further fixes with -Ywarn-unused included
SI-8916 Revert addition of -Ywarn-unused[-import]

  -Ywarn-unused-import: creates a bogues warning, see SI-7750

  -Ywarn-unused: creates a lot of noise & has bugs, see SI-7707, SI-7712
Merge pull request #4054 from soc/SI-8916

SI-8916 Clean up unused imports, values and variables