Remove "Elastic Agent to Fleet" default port assignments

[kilfoyle]

This updates the documented default port assignments to remove mention of Agent -> Fleet communication, since Agent only communicates with Fleet via Fleet Server.

Rel: #1075

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Deploy on Elastic Cloud
Elastic Agent → Fleet Server | 443
Elastic Agent → Elasticsearch | 443
Elastic Agent → Logstash | 5044
Elastic Agent → Fleet 443
Fleet Server → Fleet 443
Fleet Server → Elasticsearch 443

Deploy Fleet Server on-premises and Elasticsearch on Cloud
Elastic Agent → Fleet Server 8220
Elastic Agent → Elasticsearch 443
Elastic Agent → Logstash 5044
Elastic Agent → Fleet 443
Fleet Server → Fleet 443
Fleet Server → Elasticsearch 443

Deploy on-premises and self-managed
Elastic Agent → Fleet Server 8220
Elastic Agent → Elasticsearch 9200
Elastic Agent → Logstash 5044
Elastic Agent → Fleet 5601
Fleet Server → Fleet 5601
Fleet Server → Elasticsearch 9200

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