Tiny simplification to read-char-by-name

Tiny simplification to read-char-by-name

* lisp/international/mule-cmds.el (mule--ucs-names-sort-by-code):
Sort with car-less-than-car instead of slower lambda.
(mule--ucs-names-affixation): Just stick character into a list to
avoid trip through format and char-to-string.
(read-char-by-name): Quote function symbols as such.