Adapt processing to almost fixed size packets

If the changes in #scouting-demonstrator/scouting-preprocessor/80 are successful SCDAQ itself will need to be adapted to this.

This means:

• Adapt check of packet end marker (it will be 0xdeadbeef instead of 0xdeadbeefdeadbeef now) (was not necessary)
• Extract packet size in frames from trailer (it will be in the place of the removed 0xdeadbeef) and use it for sanity checks
• Remove packet size in orbits configuration setting as well as sanity checks