src: use SPDX identifiers The SPDX identifiers [1] are a legally binding shorthand, which can be used instead of the full boiler plate text. This is another step towards implementing the full REUSE spec [2] to help with copyright and licensing audits and compliance. This will reduce a lot a manual work required for the licensing audit required in Debian on each update. [1] https://spdx.org/ids-how [2] https://reuse.software/tutorial/ Change-Id: Ia28ed8c14984ac9acd140ef544fd6e09b96fb03b Signed-off-by: Michael Jeanson <mjeanson@efficios.com> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>