docs: Update license information in README and meson.build
Some of the files in malcontent-control
are GPL-2.0+.
Use the latest SPDX identifiers in the machine-readable data in meson.build, but use the deprecated ‘+’ form in the README since it’s a little more human friendly.
See https://spdx.org/licenses/.
Signed-off-by: Philip Withnall withnall@endlessm.com