[mus+ash] Removes WmWindow from ash/wm/focus_rules

With this CL WmWindow is no longer used in ash/wm.

BUG=722553
TEST=None (refactoring)

Review-Url: https://codereview.chromium.org/2908643003
Cr-Commit-Position: refs/heads/master@{#475121}
diff --git a/ash/mus/shell_delegate_mus.cc b/ash/mus/shell_delegate_mus.cc
index 9a4fb29..b068bc9 100644
--- a/ash/mus/shell_delegate_mus.cc
+++ b/ash/mus/shell_delegate_mus.cc
@@ -71,7 +71,7 @@
   return false;
 }
 
-bool ShellDelegateMus::CanShowWindowForUser(WmWindow* window) const {
+bool ShellDelegateMus::CanShowWindowForUser(aura::Window* window) const {
   NOTIMPLEMENTED();
   return true;
 }