Remove LOCAL_CERTIFICATE := platform from overlay packages

Bug: 129376306
Test: builds and runs

$ find . -name Android.mk | xargs sed -i 's/LOCAL_CERTIFICATE.*//g'

Change-Id: I70cb4719e6b675477b858f043f31095a9dedbdcd
diff --git a/packages/overlays/DisplayCutoutEmulationDoubleOverlay/Android.mk b/packages/overlays/DisplayCutoutEmulationDoubleOverlay/Android.mk
index 7042906..8ca2dad 100644
--- a/packages/overlays/DisplayCutoutEmulationDoubleOverlay/Android.mk
+++ b/packages/overlays/DisplayCutoutEmulationDoubleOverlay/Android.mk
@@ -2,7 +2,7 @@
 include $(CLEAR_VARS)
 
 LOCAL_RRO_THEME := DisplayCutoutEmulationDouble
-LOCAL_CERTIFICATE := platform
+
 
 LOCAL_PRODUCT_MODULE := true