Rename `SenderData` to `SenderDataTBE`

[TWal]

With the renaming in #839, some message formats used before encryption / after decryption were suffixed with TBE (with the same spirit as TBS). However SenderData is only used before encryption / after decryption, so it makes sense to add TBE in the name, hence this pull request.

[Bren2010]

Honestly I'd prefer not to have the extra cruft

[TWal]

I'm not opposed to leave SenderData as-is, but I think the whole document should have a consistent naming convention: either every message format used as input for encryption/decryption has TBE suffixed, or none of them has. A middle-ground where some are named with TBE and some aren't is not great I think.

[bifurcation]

I am also disinclined to do this. We have the following structs that are inputs:

• GroupSecrets
• GroupInfo
• SenderData
• PrivateMessageTBE

If anything, I would be inclined to remove the TBE. Maybe call it PrivateMessageContent.

[TWal]

Thanks for the exhaustive list! Dropping the TBE makes sense. I think the difference between TBE and TBS/TBM is that xxxTBS and xxxTBM are always linked to another message format xxx, which is not the case of xxxTBE.

[TWal]

Closing in favor of #870.