drm_hwcomposer: Clean up SetLayerBlendMode for hwc3

Don't use the existing HWC2 api. Remove related hwc2/hwc3 conversion
helper.

Change-Id: Ie3e53d1854df2e895360bd0c445d398649ab310a
Signed-off-by: Drew Davenport <ddavenport@google.com>
diff --git a/hwc2_device/HwcLayer.cpp b/hwc2_device/HwcLayer.cpp
index da4ce7c..e2b20f4 100644
--- a/hwc2_device/HwcLayer.cpp
+++ b/hwc2_device/HwcLayer.cpp
@@ -24,6 +24,12 @@
 
 namespace android {
 
+void HwcLayer::SetLayerProperties(const LayerProperties& layer_properties) {
+  if (layer_properties.blend_mode) {
+    blend_mode_ = layer_properties.blend_mode.value();
+  }
+}
+
 // NOLINTNEXTLINE(readability-convert-member-functions-to-static)
 HWC2::Error HwcLayer::SetCursorPosition(int32_t /*x*/, int32_t /*y*/) {
   return HWC2::Error::None;