board-js2x: fix release build process

To create a relase for the PowerStation following command should
be used: make -s driver BOARD=js2x CC=gcc342
The "driver" target also wanted to build the image for an
external flasher. The script creating this binary is, however,
not part of IBM's SLOF open source release. Therefore it has
been removed from the Makefile.
This change also removes the "changes.txt" from the binary
release tarball.
1 file changed