[UII] Agent-based deployment mode doesn't get disabled if it is not available

[jen-huang]

Integration Box connectors only has agentless deployment mode available:

"deployment_modes": {
  "default": {
    "enabled": false
  },
  "agentless": {
    "enabled": true,
    "organization": "elastic",
    "division": "engineering",
    "team": "search-extract-and-transform"
  }
}

The UI correctly selects agentless by default, but agent-based is still able to be selected:

Deployments that are not available should be disabled instead.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)