copilot-theorem: Removed unnecessary dependency on parsec. Refs #661.

The function `copilot-theorem:Copilot.Theorem.Misc.SExpr.parseSExpr` is
not used anywhere in the implementation. The module is internal and not
exposed to the user, so that function does not have and cannot have any
users.

A prior commit has removed the function, which was the only user of the
`parsec` library across `copilot-theorem`, thus rendering that
dependency no longer necessary.

This commit removes that dependency from the Cabal file.

Author: ivanperez-keera

copilot-theorem/copilot-theorem.cabal

@@ -54,7 +54,6 @@ library
                           , libBF                 >= 0.6.2 && < 0.7
                           , mtl                   >= 2.0 && < 2.4
                           , panic                 >= 0.4.0 && < 0.5
-                          , parsec                >= 2.0 && < 3.2
                           , parameterized-utils   >= 2.1.1 && < 2.2
                           , pretty                >= 1.0 && < 1.2
                           , process               >= 1.6 && < 1.7