schema: Remove satellite field from DemodData model

The database schema, here specifically the DemodData model, should be redesigned to make it easier to create a proper API.

💡 Feature request

As @acinonyx wrote in the forum:

The DemodData model has satellite and transmitter fields in DemodData but the transmitter also has a satellite field (as FK) creating a circular relationship.

To fix this the satellite field should be removed from the DemodData model.

🎯 Goal

• Simplify the database schema
• Remove the circular relationship
• Prevent data corruption cases in which DemodData.satellite != DemodData.transmitter.satellite