remove MaxStep from Soccer agents (#5310)

Project/Assets/ML-Agents/Examples/Soccer/Prefabs/SoccerFieldTwos.prefab

   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  MaxStep: 3000
+  MaxStep: 0
   team: 0
   position: 2
   agentRb: {fileID: 0}
   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  MaxStep: 3000
+  MaxStep: 0
   team: 1
   position: 2
   agentRb: {fileID: 0}
   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  MaxStep: 3000
+  MaxStep: 0
   team: 0
   position: 2
   agentRb: {fileID: 0}
   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  MaxStep: 3000
+  MaxStep: 0
   team: 1
   position: 2
   agentRb: {fileID: 0}

Project/Assets/ML-Agents/Examples/Soccer/Prefabs/StrikersVsGoalieField.prefab

   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  MaxStep: 3000
+  MaxStep: 0
   team: 0
   position: 1
   agentRb: {fileID: 0}
   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  MaxStep: 3000
+  MaxStep: 0
   team: 1
   position: 0
   agentRb: {fileID: 0}
   agentParameters:
     maxStep: 0
   hasUpgradedFromAgentParameters: 1
-  MaxStep: 3000
+  MaxStep: 0
   team: 1
   position: 0
   agentRb: {fileID: 0}