Use only the intrinsic version (eg. 1.0.0) instead of the extrinsic version
(eg. stretch/contrib/1.0.0).
Releases should only contain data from DSC, not external 'pointers' to them.
Additionally, having extrinsic data in releases means the same
dsc-sha256 extid can point to different releases, which meant the loader
may reuse a release mentioning a specific suite as a release in a
different suite.
With this commit, this won't be a problem anymore, as releases won't
mention the suite at all, so suites can safely share extids.
Depends on D6748
**Note: this diff fixes data corruption, that at best crashes the loaders,
at worst makes them write wrong stuff. In order to fix it, we need to wipe
all ExtIDs from the database with type `dsc-sha256` pointing to a release SWHID.**