Re: unload-feature and defcustom.

[Richard Stallman]

    (require 'a)
    (unload-feature 'a)

    Now a-cus-var is not bound, but when I do M-x customize-option, I can
    still select (with completion) a-cus-var and that gives me this
    customization buffer:

I think the cleaner fix is to undo more of what the defcustom
did, so that the variable can't be customized.  That could be
fixed in unload-feature.  You just need to figure out which
properties ought to be removed and which should not be.