Replace expensive unique-like implementations

[philderbeast]

cabal/Cabal-tests/tests/UnitTests/Distribution/PackageDescription/Check.hs

Line 29 in c3c060f

uniqueNames = length allExplanationIdStrings == length (nub allExplanationIdStrings)

Spotted by @Bodigrim when reviewing #11825. Please see the thread starting with #11825 (comment) for more detail.

Functions to check and mentioned in that thread are the above and the following;

cabal/Cabal-tests/tests/UnitTests/Distribution/Compat/Graph.hs

Lines 64 to 71 in e7aaad8

	hasNoDups :: Ord a => [a] -> Bool
	hasNoDups = loop Set.empty
	where
	loop _ [] = True
	loop s (x:xs) | s' <- Set.insert x s, Set.size s' > Set.size s
	= loop s' xs
	| otherwise
	= False

cabal/cabal-install/tests/UnitTests/Distribution/Client/UserConfig.hs

Lines 93 to 96 in e7aaad8

	listUnique :: Ord a => [a] -> Bool
	listUnique xs =
	let sorted = sort xs
	in nub sorted == xs

cabal/cabal-install/tests/UnitTests/Distribution/Solver/Modular/WeightedPSQ.hs

Lines 52 to 54 in e7aaad8

	isSorted :: Ord a => [a] -> Bool
	isSorted (x1 : xs@(x2 : _)) = x1 <= x2 && isSorted xs
	isSorted _ = True

cabal/solver-benchmarks/HackageBenchmark.hs

Lines 351 to 352 in e7aaad8

	allEqual :: Eq a => [a] -> Bool
	allEqual xs = length (nub xs) == 1

cabal/cabal-install-solver/src/Distribution/Solver/Modular/Linking.hs

Lines 518 to 521 in e7aaad8

	allEqual :: Eq a => [a] -> Bool
	allEqual [] = True
	allEqual [_] = True
	allEqual (x:y:ys) = x == y && allEqual (y:ys)