classes/populate_sdk_ext: drop ext-sdk-prepare.py when installing
At the end of the extensible SDK installation, if we've successfully
prepared the build system then we don't need ext-sdk-prepare.py. I had
thought earlier that this would be used when updating, but a different
mechanism was needed there so this script isn't used for that.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
