Remove some unused make vars

These vars were exported by soong so that kati can generate installation
rules for these artifacts. With https://r.android.com/3272600, soong
will create the installation rules, therefore exporting these variables
is no longer necessary.

Test: m nothing --no-skip-soong-tests
Test: No diff in system_intermediates/file_list.txt
Change-Id: I949976024e22b297d261ab7eb6354d8e77f1b34e