Re: read-face-name PROMPT arg should be self-contained, including ": "

[Richard Stallman]

    `read-face-name' still blindly appends ": " to the prompt it is supplied.

I thought of `read-face-name' as an internal function, not for users to use.
But I agree that it could be useful for user code to call.
So I'm not against making this change.  I see that all the callers
within Emacs are easy to change.

If someone wants to do it, please do it.