default_log_handler.h unclear license

[fmauch]

The default_log_handler.h file has an unclear license statement. While it is explicitly licensed under Apache-2.0 the capitalized text below doesn't belong to the Apache-2.0 license header. Furthermore it seems to be very similar to MIT's license header which is why license scanners such as scancode-toolkit seem to detect an MIT license in that header.

@urmahp what was the reason for adding this paragraph? @urrsk would you be OK with removing that paragraph and only keep the Apache-2.0 header?

[urrsk]

Yes, but I will prefer BSD3 instead if possible to mix.
Going forward we should, if possible, publics under bsd3