Consolidate license headers

[robin-nitrokey]

Some files use license headers like this one:

nitrokey-sdk-py/src/nitrokey/nk3/__init__.py

Lines 1 to 6 in 6773178

	# Copyright 2021-2022 Nitrokey Developers
	#
	# Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
	# http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
	# http://opensource.org/licenses/MIT>, at your option. This file may not be
	# copied, modified, or distributed except according to those terms.

We should either remove them or consistently use SPDX license headers.