Remove all the extensions to string-upcase and friends. The extended

functions now live in the new UNICODE package.

 src/code/exports.lisp::
 * Export some unicode functions and constants.

 src/code/string.lisp::
 * Removed the extended versions of string-upcase and friends.
 * Export surrogates function.
 * Make sure with-one-string is defined so the unicode package can use
   it.

 src/code/unicode.lisp:;
 * New file with extended versions of string-upcase and friends.

 src/code/unidata.lisp::
 * Export some unicode functions and constants.

 src/compiler/fndb.lisp::
 * Update defknowns for string-upcase and friends.

 src/tools/worldbuild.lisp::
 * Build unicode.lisp

 src/tools/worldcom.lisp::
 * Load unicode.lisp