hadrian: Cabal verbosity is too high

See: https://gitlab.haskell.org/ghc/ghc/-/jobs/1752376

Over 5000 lines are devoted to the verbose output of cabal copy, this is too high.

The comment claims that simpleUserHooks decreases verbosity, and it
does, but only for the postConf phase. The other phases are too
verbose with -V.

So I take the simple approach and just decrease the verbosity level again.

If the output of postConf is essential then it would be better to
implement our own UserHooks which doesn't decrease the verbosity for
postConf.

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