Unset PRODUCT_INSTALL_DEBUG_POLICY_TO_SYSTEM_EXT for gsi_car_${arch}.mk

These options are only meant for the phone GSI, and causes errors here,
so clear the variable value.

Bug: 188067818
Test: Presubmit
Change-Id: I96fe6556a3c305b80013b9523089c26ecbf9ffd8
Merged-In: I96fe6556a3c305b80013b9523089c26ecbf9ffd8
(cherry picked from commit 9170a9457953a30657c66b5368d8d600055cf190)
2 files changed