hydra: Ensure analysis payload is set to None when facing an analysis error

[maudetes]

When we encounter a "File too large to download" on analysis, we only send the payload with analysis:error to udata and don't remove previous keys that may become irrelevant (analysis:checksum, analysis:last-modified-at etc.).

Indeed, extras update in udata has a dict update policy and a strip of keys with None value.

We should make sure to remove other analysis keys when facing an error by adding them in payload with None value.
Indeed, when a file has been analyzed but is now bigger than the limit, previous extras will be kept forever in udata.

On the contrary, on a successful analysis, we should make sure to remove eventual existing analysis:error by setting to None.