beckham: Disable screen mirroring dialog

* Our Moto Mod Projector app doesn't like it, so users can't interact with this dialog.

Change-Id: I21567a85c439597a506475a4f884a75e5312356a
(cherry picked from commit 30b572c347403bdd28dcaa2160f6adb5c5bbc74a)
(cherry picked from commit 8d9fd39bbb2334b307868e79c92b9617258e3510)

system_ext.prop

 # Audio
 ro.qc.sdk.audio.fluencetype=none
+
+# Display Mirroring Dialog
+persist.sysui.disable_mirroring_confirmation_dialog=true