Replace use of tail with drop 1 in PlutusTx/Enum/TH.hs

[zeme-wana]

Fixes this error:

src/PlutusTx/Enum/TH.hs:53:59: error: [GHC-63394] [-Wx-partial, -Werror=x-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
53 |       [ funD 'succ (fmap (deriveSuccPred Succ) (zip cons (tail (Just <$> cons) ++ [Nothing])))
   |     

[kwxm]

Is there any danger that this will actually get an empty list, or is the input guaranteed to be non-empty -in this situation? drop 1 [] is [], which might not be what we want. Matching on the list and failing for the empty list (which may be impossible) might be safer.