bug#30186: 27.0.50; Password is not hidden in read-passwd

[Juri Linkov]

This is a regression and a security flaw.

Reading a password with ‘read-passwd’ doesn't hide inserted characters
anymore as it used to do in older versions.

When the user has such customization:

  (custom-set-variables
   '(yank-excluded-properties t))

evaluating

  (read-passwd "Prompt: ")

and yanking a password to the minibuffer with 'C-y' doesn't hide it
as it did in Emacs 25.

This can be traced down to ‘remove-yank-excluded-properties’
where ‘set-text-properties’ used to leave ‘display’ properties
(with ‘.’ over inserted characters) in the minibuffer.