speculate.cabal: remove plus-abs benchmark

it is included in extra-source-files anyway.

This makes it so that we don't need the test/sdist Hack now.

A bug has nevertheless been reported to the cabal team:

haskell/cabal#6611

speculate.cabal

@@ -180,13 +180,6 @@ test-suite utils
   default-language:  Haskell2010
   type:              exitcode-stdio-1.0
 
-benchmark plus-abs
-  main-is:           plus-abs.hs
-  hs-source-dirs:    eg
-  build-depends:     base >= 4 && < 5, speculate
-  default-language:  Haskell2010
-  type:              exitcode-stdio-1.0
-
 benchmark test-stats
   main-is:           stats.hs
   other-modules:     Test, Test.ListableExpr

test/sdist

@@ -25,19 +25,16 @@ pkg=`find dist* -name $pkgbase.tar.gz`
 tmp=`mktemp -d /tmp/test-sdist-XXXXXXXXXX`
 
 # Test if our file is compatible with case-insensitive filesystems.
-tar -tf $pkg | sort -u | sort --ignore-case          > $tmp/ls-cabal-i
-tar -tf $pkg | sort -u | sort --ignore-case --unique > $tmp/ls-cabal-iu
+tar -tf $pkg | sort --ignore-case          > $tmp/ls-cabal-i
+tar -tf $pkg | sort --ignore-case --unique > $tmp/ls-cabal-iu
 diff -rud $tmp/ls-cabal-i $tmp/ls-cabal-iu
 
 if [ -d .git ]
 then
 	# Test if files included by cabal are the same as files tracked in git.
 	git ls-files                                         | sort > $tmp/ls-git
-	tar -tf $pkg | sort -u | grep -v "/$" | sed -e "s,$pkgbase/,," | sort > $tmp/ls-cabal
+	tar -tf $pkg | grep -v "/$" | sed -e "s,$pkgbase/,," | sort > $tmp/ls-cabal
 	diff -rud $tmp/ls-git $tmp/ls-cabal
 fi
 
 rm -r $tmp
-
-# NOTE: above the "sort -u" is only needed because of a bug in cabal:
-# the "plus-abs.hs" file is included twice for some reason...