Refactor RenderState and remove unused functionality.

Test: hwui_unit_tests still pass
Change-Id: Ie943671535ab8c5da1bac05985e815e0cb842dc1
diff --git a/libs/hwui/RenderNode.cpp b/libs/hwui/RenderNode.cpp
index d5afb20..896b434 100644
--- a/libs/hwui/RenderNode.cpp
+++ b/libs/hwui/RenderNode.cpp
@@ -158,7 +158,7 @@
         CC_UNLIKELY(properties().getWidth() == 0) || CC_UNLIKELY(properties().getHeight() == 0) ||
         CC_UNLIKELY(!properties().fitsOnLayer())) {
         if (CC_UNLIKELY(hasLayer())) {
-            renderthread::CanvasContext::destroyLayer(this);
+            this->setLayerSurface(nullptr);
         }
         return;
     }
@@ -313,7 +313,7 @@
 
 void RenderNode::destroyHardwareResources(TreeInfo* info) {
     if (hasLayer()) {
-        renderthread::CanvasContext::destroyLayer(this);
+        this->setLayerSurface(nullptr);
     }
     setStagingDisplayList(nullptr);
 
@@ -323,7 +323,7 @@
 
 void RenderNode::destroyLayers() {
     if (hasLayer()) {
-        renderthread::CanvasContext::destroyLayer(this);
+        this->setLayerSurface(nullptr);
     }
     if (mDisplayList) {
         mDisplayList->updateChildren([](RenderNode* child) { child->destroyLayers(); });