Move ess-smart-equals to ess-packages

This way it is always discoverable in helm-spacemacs
the :if keyword of use-package allow to enable it on demande with
ess-enable-smart-equals

contrib/lang/ess/packages.el

@@ -15,14 +15,12 @@
     ess
     ess-R-data-view
     ess-R-object-popup
+    ess-smart-equals
     rainbow-delimiters
     )
   "List of all packages to install and/or initialize. Built-in packages
 which require an initialization must be listed explicitly in the list.")
 
-(when ess-enable-smart-equals
-  (add-to-list 'ess-packages '(ess-smart-equals)))
-
 (defvar ess-excluded-packages '()
   "List of packages to exclude.")