Undo a buggy change in ParseUtils

A change in commit https://github.com/haskell/cabal/commit/1ecd69c7127be446b42e736d72b5d6956a40db52 causes ppField to generate lines which contain only a four space indent, no "." and no other text.  This causes failures.  I've reported the issue in https://github.com/haskell/cabal/issues/1921.  This patch reverts the change, but it would be good if an improved version of this change could be submitted.