Remove some declare-function stub definitions

Remove some declare-function stub definitions

* lisp/emulation/viper-cmd.el, lisp/emulation/viper-keym.el:
* lisp/emulation/viper-util.el, lisp/net/newst-plainview.el:
* lisp/net/newst-treeview.el, lisp/ps-def.el, lisp/vc/ediff.el:
* lisp/vc/ediff-util.el, lisp/vc/ediff-wind.el:
Remove stub declare-function definitions.
It exists since Emacs 22.2, released 10 years ago.
Most of these files are using even newer features, such as
lexical-binding and cl-lib anyway, making the stubs pointless.