Prevent the focus state from getting cleared

Before this CL, if the ViewRootImpl receives an input event after
adding the window to display before performing its first traversal,
mAttachInfo.mHasWindowFocus would be set to true in
handleWindowFocusChanged called by deliverInputEvent. And then, when
ViewRootImpl is performing its first traversal,
mAttachInfo.mHasWindowFocus would be cleared, which would make the
ViewRootImpl drop all the key events.

This CL removes the redundant logic about clearing
mAttachInfo.mHasWindowFocus during the first traversal.

Bug: 119700105
Test: atest WindowFocusTests
Change-Id: Ic35752f8e0d7cd7899f238e184bfbca3c8f7ad08