Do not call build/envsetup.sh in create_reference_dumps

This commit makes get_build_vars_for_product get variables by
soong_ui.bash without envsetup.sh.

Bug: 120819347
Test: ./create_reference_dumps.py --llndk -libs libbinder_ndk
Change-Id: I66d1245d277d3c5459c6027ccdb88288aaf4d802