In meta/classes/create-spdx.bbclass, the SPDX_INCLUDE_PACKAGED variable is read into the "include_packaged" variable, which doesn't appear anywhere else. As a consequence, this variable has no effect. This could be a bug, this variable corresponding to functionality that is supposed to be implemented. Otherwise, let's just remove the unnecessary dead code.
Doc changes will be necessary if the code is fixed and eventually does something.
Bug now closed thanks to https://git.openembedded.org/openembedded-core/commit/?id=89f1abd5e00807cf179ddf658f74d48119523b0c No doc changes as this didn't get documented.