Ensure deviceTimestamp is cleared

Add native test to ensure that deviceTimestamp field
is cleared.

Bug: 62940136
Test: m -j inputflinger_tests_InputReader_test
inputflinger_tests_InputDispatcher_test && adb push
out/target/product/$TARGET_PRODUCT/data/nativetest64/*
/data/nativetest64/
(adb shell mkdir /data/nativetest64 if needed)
on device: /data/nativetest64/inputflinger_tests # ./InputReader_test

Change-Id: Id70f07b143c22fc337fa94b264bc7fafa3f8d3fd