Revert two commits for bug#19032

This reverts:

- commit 585fe00557, which is titled
  "Fix up previous icomplete-show-matches-on-no-input change"

- commit 1b8d369c38, which is titled
  "Change icomplete-show-matches-on-no-input behavior".

A simpler, less intrusive fix follows shortly after this commit.

lisp/icomplete.el

@@ -75,11 +75,7 @@ everything preceding the ~/ is discarded so the interactive
 selection process starts again from the user's $HOME.")
 
 (defcustom icomplete-show-matches-on-no-input nil
-  "When non-nil, show completions when first prompting for input.
-This also means that if you traverse the list of completions with
-commands like `C-.' and just hit `C-j' (enter) without typing any
-characters, the match under point will be chosen instead of the
-default."
+  "When non-nil, show completions when first prompting for input."
   :type 'boolean
   :version "24.4")
 
@@ -755,10 +751,7 @@ matches exist."
 		(push comp prospects)
 	      (setq limit t))))
 	(setq prospects (nreverse prospects))
-        ;; Return the first match if the user hits enter.
-        (when icomplete-show-matches-on-no-input
-          (setq-local completion-content-when-empty (car prospects)))
-        ;; Decorate first of the prospects.
+	;; Decorate first of the prospects.
 	(when prospects
 	  (let ((first (copy-sequence (pop prospects))))
 	    (put-text-property 0 (length first)