go-helloworld: fix license

go-helloworld: fix license

The example repo doesn't seem to have ever been under MIT to begin with
but rather Apache-2.0. It was then changed to the license used by the
goland projectm that is BSD-3-Clause, 2 years ago in commit 00c7068f9d83
("all: update to Go license").

The license file exists in the sources, so use that one instead of
taking it from the OE-Core license directory.

License-Update: Incorrect license is now proper

Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Signed-off-by: Steve Sakoman <steve@sakoman.com>