Revert "avrdude: add license information"

This reverts commit d1f54500 from 2014
because the added variables already existed. The real problem at the
time was that one of the pre-existent variables had a typo, fixed in a
later commit.

Currently AVRDUDE_LICENSE and AVRDUDE_LICENSE_FILES are declared twice
with the same values for each one. So remove one of them.

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Cc: Wojciech M. Zabolotny <wzab01@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>