Hadrian turns on `-Wno-unused-imports` for text when using integer-simple

In Settings.Warnings, hadrian turns on -Wno-unused-imports for the text package when building with integer-simple.

It would be good to fix text so we can remove this special case.

1. Build GHC with integer-simple and -Werror
2. Remove the special case for text in Settings.Warnings.
3. Fix the warnings in text appropriately so the build finishes.
4. Push the fix upstream and then update the submodule.

This could also be debugged without having to build ghc by downloading an integer-simple bindist.

Also see: https://github.com/haskell/text/issues/250

Trac metadata

Trac field	Value
Version	8.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Build System (Hadrian)
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