Remove needless quotes from keylist of case macro

[syohex]

Development Emacs(29.0.50) generates following byte-compile warnings. This PR fixes warnings like below ones.

haskell-cabal.el:704:12: Warning: Case 'before will match ‘quote’.  If that’s
    intended, write (before quote) instead.  Otherwise, don’t quote ‘before’.
haskell-cabal.el:704:12: Warning: Case 'after will match ‘quote’.  If that’s
    intended, write (after quote) instead.  Otherwise, don’t quote ‘after’.
haskell-cabal.el:704:12: Warning: Case 'single will match ‘quote’.  If that’s
    intended, write (single quote) instead.  Otherwise, don’t quote ‘single’.

[purcell]

Super, thank you!