Remove undefined PRIVATE_* variable

This variable isn't defined for $(jack_lib), and isn't needed, since we
haven't created our intermediate directory at this point.

Test: Run in different configurations (no options, dist tests), make
      sure this command line doesn't change.
Change-Id: Ie863e1e632a9b6eb343b3f411f6c6cc548fa2a2c
1 file changed