Remove $(module)_install_to_out_data flag from test makefile

Use non-empty $(module)_install_to_out_data_dir as indication
of custom target dir for a library.

Bug: http://b/22182538
Test: build and run bionic-unit-tests --gtest_filter=dl*:Dl*
Change-Id: Ibfc87f45084a6fe2f487ca1b17a7625a8d8ec707