SF: BufferStateLayer cleanup

Clean up some of the logic now that
BufferLayer has been merged into BufferStateLayer.

Test: presubmit
Bug: 238781169
Change-Id: I5114dd8d457638f810fe02d29bfab3444e042d2d
diff --git a/services/surfaceflinger/tests/unittests/CachingTest.cpp b/services/surfaceflinger/tests/unittests/CachingTest.cpp
index 6f85498..7f203ce 100644
--- a/services/surfaceflinger/tests/unittests/CachingTest.cpp
+++ b/services/surfaceflinger/tests/unittests/CachingTest.cpp
@@ -26,8 +26,7 @@
 
 class SlotGenerationTest : public testing::Test {
 protected:
-    sp<BufferStateLayer::HwcSlotGenerator> mHwcSlotGenerator =
-            sp<BufferStateLayer::HwcSlotGenerator>::make();
+    sp<HwcSlotGenerator> mHwcSlotGenerator = sp<HwcSlotGenerator>::make();
     sp<GraphicBuffer> mBuffer1{new GraphicBuffer(1, 1, HAL_PIXEL_FORMAT_RGBA_8888, 1, 0)};
     sp<GraphicBuffer> mBuffer2{new GraphicBuffer(1, 1, HAL_PIXEL_FORMAT_RGBA_8888, 1, 0)};
     sp<GraphicBuffer> mBuffer3{new GraphicBuffer(10, 10, HAL_PIXEL_FORMAT_RGBA_8888, 1, 0)};