(viper-read-key, viper-read-key-sequence): Remove

(viper-read-key, viper-read-key-sequence): Remove

Ever since the time-dependent ESC handling was moved to input-decode-map,
viper-read-key-sequence has been obsolete.  Clean up accordingly.

* lisp/emulation/viper-keym.el: Use lexical-binding.
(viper-overriding-map): Remove.

* lisp/emulation/viper-macs.el: Use lexical-binding and 'read-key'.

* lisp/emulation/viper-util.el: Use lexical-binding.
(viper-read-key, viper-read-key-sequence): Remove.

* lisp/emulation/viper.el (viper-non-hook-settings): Remove obsolete advice.