aura: Remove unused Window::Blur().

The last use of Window::Blur() was removed recently (crrev.com/329087). So
remove it now.

BUG=none

Review URL: https://codereview.chromium.org/1135063002

Cr-Commit-Position: refs/heads/master@{#329168}

ui/aura/window.cc

@@ -675,12 +675,6 @@ void Window::Focus() {
   client->FocusWindow(this);
 }
 
-void Window::Blur() {
-  client::FocusClient* client = client::GetFocusClient(this);
-  DCHECK(client);
-  client->FocusWindow(NULL);
-}
-
 bool Window::HasFocus() const {
   client::FocusClient* client = client::GetFocusClient(this);
   return client && client->GetFocusedWindow() == this;

ui/aura/window.h

@@ -266,9 +266,8 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   // that has a delegate set).  The toplevel window may be |this|.
   Window* GetToplevelWindow();
 
-  // Claims or relinquishes the claim to focus.
+  // Claims focus.
   void Focus();
-  void Blur();
 
   // Returns true if the Window is currently the focused window.
   bool HasFocus() const;