Drop SDK 19 tests (1)

Summary:
The next Robolectric release drops support for SDK 19 (KitKat). Nearly all apps are min SDK 21+ anyway.

The strategy here:
- If a test was explicitly designed to test a pre-21 code path, just remove it
- If the test passes on the latest SDK, just remove the SDK-19 config
- else, pin the test on SDK 21, punting the issue.

Reviewed By: jiawei-lyu

Differential Revision: D59967783

fbshipit-source-id: 4b81074b532042cf58872bcb7e6e35dc1c83a9bf

litho-rendercore-incremental-mount/src/test/java/com/facebook/rendercore/incrementalmount/IncrementalMountExtensionTest.kt

@@ -47,7 +47,6 @@ import org.robolectric.RobolectricTestRunner
 import org.robolectric.annotation.Config
 
 @RunWith(RobolectricTestRunner::class)
-@Config(sdk = [19])
 class IncrementalMountExtensionTest {
   @Rule @JvmField val renderCoreTestRule = RenderCoreTestRule()
 
@@ -305,6 +304,7 @@ class IncrementalMountExtensionTest {
   }
 
   @Test
+  @Config(sdk = [21])
   fun whenPreviousHostIsMovedOutOfBounds_shouldMountItemsCorrectly() {
     val c = renderCoreTestRule.context
     val parent = FrameLayout(c)