Don't pause display for pending input

Don't pause display for pending input

* src/dispnew.c: Remove display_completed, redisplay_dont_pause,
redisplay-dont-pause was declared obsolete in Emacs 24.  Remove anything
checking pending input, change function signatures accordingly, and so
on.

* src/keyboard.c (read_char): Don't use redisplay_dont_pause.
* src/minibuf.c (read_minibuf): Use new function signatures.
* src/xdisp.c: Don't check display_completed. Use new API.

* lisp/subr.el (redisplay-dont-pause): Remove declaration.

(cherry picked from commit f62d70f52f4f6b7ed158d618bf790df21f171172)