Clean up isVisibleLw and isDimming of WindowManagerPolicy#WindowState

The isVisibleLw just redirects to call isVisible. These methods were
used for PhoneWindowManager to access wm package. Since all usages
are removed, the interface methods are no longer needed.

Bug: 163976519
Test: WmTests CtsWindowManagerDeviceTestCases presubmit
Change-Id: I29521e806fb42c0b54caa82e103291cc74130899