Clean up android.hardware.automotive.vehicle intermediates.

In ag/20886210, the VHAL properties were separated into a new AIDL
interface but the names remained the same.  In incremental builds with
pre-existing old versions of AIDL, these generated headers would remain
there and gets picked up due to include directory ordering.

Eliminate this possiblity by performing a cleanup of the generated
primary headers directory.

Merged-In: Ic5ef401b427b2772e8527b2dc9804781a51125be
Change-Id: Ic5ef401b427b2772e8527b2dc9804781a51125be