Remove additional_info data structure

[mj]

Prior to this change esp-knx-ip did not compile for me in Arduino 1.8.19 on macOS Monterey. The build failed with

In file included from /path/to/Project.ino:1:
esp-knx-ip.h:259:17: error: flexible array member in union
  259 |     cemi_addi_t additional_info[];
      |                 ^~~~~~~~~~~~~~~
exit status 1
flexible array member in union

In addition to that the additional_info array does not seem to be actively used anywhere in the code. So all in all this change seems fine to me.

[IonasElate]

Great solution. i was running into the same difficulties and manually commented the lines out you highlighted.