If you only have one probability value (a single "P" value, rather than separate P1 and P2 values), you can configure your total probability risk matrix in Ketryx by "obsoleting" one of the probability values. This means you set only one option for the unused value (e.g., "N/A"), so your remaining probability value (P) is directly mapped to the total probability. This can be configured via the risk configuration at the project and organizational level. Please see the supporting FAQ here. 

Removing individual fields of the initial / residual risk analysis sections (ex. P1 or P2) is not supported. 
You may remove other fields like the risk control options or other fields unrelated to risk analysis through the itemFields advanced setting at the organizational level. 

For example: 

 "Risk": {
    "removedFields": [
      "riskControlOptions"
    ]
  }