Remove instance Binary Char

Depends on !10403 (closed)

Still needs some haddock changes, putting this up for review before making them.

It is generally not a good idea to serialise strings as [Char] into interface files, as upon deserialisation each of these would be turned into a highly memory inefficient structure mostly composed of cons cells and pointers.

If you really want to serialise a Char, you can use the newly added SerialisableChar newtype.