Remove includes from .cabal-file

[sol]

This is useless at best, and a common source of confusion.

haskell/cabal#10145
sol/hpack#355

[kazu-yamamoto]

I need to understand why CI fails on Windows.

[kazu-yamamoto]

@sol With this patch, the following error occurs on Windows:

Error: cabal.exe: Bad header file: afunix_compat.h

[sol]

@kazu-yamamoto that's interesting, let me investigate.

[sol]

The full message is:

Bad header file: afunix_compat.h
The header file contains a compile error. You can re-run configure with the
verbosity flag -v3 to see the error messages from the C compiler.

Which is generated here: https://github.com/haskell/cabal/blob/bf6f26dc2c02cce24b0d0f429b1b0fdabaa14028/Cabal/src/Distribution/Simple/Errors.hs#L656-L658

Which I think originates from here: https://github.com/haskell/cabal/blob/bf6f26dc2c02cce24b0d0f429b1b0fdabaa14028/Cabal/src/Distribution/Simple/Configure.hs#L2546-L2569

@mpilgrem so it seems that while includes is effectively ignored and never passed to ghc nor gcc, Cabal still tries to "validate" those headers in some way, likely for historic reasons (some of the code is really old).

[sol]

@kazu-yamamoto 6e0c76a fixes the windows build, but I just noticed that you already discovered that yourself in #583.

[kazu-yamamoto]

@sol Sorry. I did not notice your latest messages.
I reached the same conclusion and merged #582.
Let's close this.
Thank you for your contribution!