core: remove wizard question about completion engine.

The default value is now at the distribution level. The user must put the ivy
layer explicitly in the dotfile.

This to be consistent with filetree package which is neotree by default in
the standard spacemacs distribution.

I'm afraid that we add too much wizard questions as the helm/ivy case will
happen more and more in the future. Neotree and Treemacs are the first layers
to follow the Helm and Ivy pattern. I don't want to add a fourth question to
the wizard which makes it heavy and is not as useful for new users.

core/core-dotspacemacs.el

@@ -586,17 +586,7 @@ If ARG is non nil then Ask questions to the user before installing the dotfile."
                     spacemacs)
                    (,(concat "A minimalist distribution that you can build on "
                              "(spacemacs-base)")
-                    spacemacs-base)))))
-             ("helm"
-              ,(dotspacemacs//ido-completing-read
-                "What type of completion framework do you want? "
-                '(("A heavy one but full-featured (helm)"
-                   "helm")
-                  ("A lighter one but still very powerful (ivy)"
-                   "ivy")
-                  ;; For now, None works only if the user selected
-                  ;; the spacemacs-base distribution
-                  ("None (not recommended)" ""))))))))
+                    spacemacs-base)))))))))
     (with-current-buffer (find-file-noselect
                           (concat dotspacemacs-template-directory
                                   ".spacemacs.template"))