Removal of repeated notes in all documentation

[stefancyliax]

I see this note repeated over and over again across all files. A quick search yields 70 hits for this exact phrase.

I do not know the original reason for including the note, but I suggest to just remove it. In my opinion, it is stating the obvious. The field is a repeated field and its name uses in fact singular. Furthermore, the above text makes it abundantly clear that there may be multiple IDs.

However, I would also suggest to add this information to the interface-conventions topic in the general documentation.

Originally posted by @max-rosin in #491 (comment)

[max-rosin]

To clarify, the note in question is:

\note OSI uses singular instead of plural for repeated field names.

It appears in the comments of the .proto files.

[PhRosenberger]

I would agree to @stefancyliax to just delete the note everywhere and have it only once in the general docu.