Remove view registry references from the workspace model layer

Removed various ::getView methods from the model. Using the atom.views
global in the views for now, but going to switch them over to using a
locally assigned view registry instead in a subsequent commit.

src/panel.coffee

@@ -14,7 +14,7 @@ class Panel
   Section: Construction and Destruction
   ###
 
-  constructor: ({@viewRegistry, @item, @visible, @priority, @className}) ->
+  constructor: ({@item, @visible, @priority, @className}) ->
     @emitter = new Emitter
     @visible ?= true
     @priority ?= 100
@@ -50,15 +50,8 @@ class Panel
   Section: Panel Details
   ###
 
-  # Public: Gets this panel model's view DOM node.
-  #
-  # Returns an `<atom-panel>` {Element}
-  getView: -> @viewRegistry.getView(this)
-
-  # Public: Gets your panel contents view.
-  #
-  # Returns an {Element} or jQuery element, depeneding on how you created the panel.
-  getItemView: -> @viewRegistry.getView(@item)
+  # Public: Returns the panel's item.
+  getItem: -> @item
 
   # Public: Returns a {Number} indicating this panel's priority.
   getPriority: -> @priority