Remove minibuffer up-to-one-word completion

Remove minibuffer up-to-one-word completion

Deprecate 'minibuffer-complete-word', and cease binding 'SPC' during
minibuffer completion altogether.

* lisp/minibuffer.el (minibuffer-complete-word): Turn it into an
obsolete alias of 'minibuffer-complete'.
(minibuffer-confirm-exit-commands): Remove 'minibuffer-complete-word'.
(completion--try-word-completion): Drop it.
(minibuffer-local-completion-map): Cease binding 'SPC'.
(minibuffer-local-filename-completion-map)
(completion-pcm-complete-word-inserts-delimiters): Deprecate.
(completion-pcm--string->pattern, completing-read-default): Simplify.

* doc/emacs/custom.texi (Minibuffer Maps)
* doc/emacs/mini.texi (Completion Commands)
* doc/lispref/help.texi (Keys in Documentation)
* doc/lispref/minibuf.texi (Completion Commands)
* lisp/emulation/viper-ex.el (viper-complete-filename-or-exit)
* lisp/gnus/mm-decode.el (mm-viewer-completion-map)
* lisp/man.el (Man-completion-table)
* lisp/menu-bar.el (map)
* test/lisp/help-tests.el (help-tests--test-keymap)
(help-tests-substitute-command-keys/keymaps): Adjust.

* etc/NEWS: Announce.