src/parser/scanner-charbuf-impl.lisp: Replace pointless use of `#.'.

src/parser/scanner-charbuf-impl.lisp: Replace pointless use of `#.'.

This only existed because `charbuf-size' is (in theory) a tweakable
constant, but `defclass' wants a literal type specifier as its `:type'
argument.  But the correct type specifier, `charbuf-index' was already
defined at the same time (both were added in the same, rather sketchy,
old commit).

It's useful to kill this because it confuses the (rather stupid) reader
in `list-exports'.