Do not call assumeTrue(isTelevision) in @After

Only call assumeTrue(isTelevision) during test setup (@Before), and do
not call it in teardown (@After), which causes tests to fail instead of
be slipped.

Bug: 171520419
Test: atest WMShellFlickerTests
Change-Id: I12f72d46a63c497686f0da7c4763ae79bbeb7dcd

libs/WindowManager/Shell/tests/flicker/src/com/android/wm/shell/flicker/pip/tv/TvPipTestBase.kt

@@ -52,7 +52,7 @@ abstract class TvPipTestBase(rotationName: String, rotation: Int)
 
     @After
     open fun tearDown() {
-        Assume.assumeTrue(isTelevision)
+        if (!isTelevision) return
 
         testApp.forceStop()