docs: remove SFMC enterprise connector stub and docs page (#74735)

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: matteo.palarchio@airbyte.io <matteo.palarchio@airbyte.io>
Co-authored-by: Matteo Palarchio <20643714+matteogp@users.noreply.github.com>

Author: devin-ai-integration[bot]

docs/integrations/enterprise-connectors/source-salesforce-marketing-cloud.md

@@ -2459,10 +2459,6 @@
     "message": "Source Oracle",
     "description": "The label for the doc item Source Oracle in sidebar connectors, linking to the doc enterprise-connectors/source-oracle-enterprise"
   },
-  "sidebar.connectors.doc.Source Salesforce Marketing Cloud Engagement": {
-    "message": "Source Salesforce Marketing Cloud Engagement",
-    "description": "The label for the doc item Source Salesforce Marketing Cloud Engagement in sidebar connectors, linking to the doc enterprise-connectors/source-salesforce-marketing-cloud"
-  },
   "sidebar.connectors.doc.Source SAP HANA": {
     "message": "Source SAP HANA",
     "description": "The label for the doc item Source SAP HANA in sidebar connectors, linking to the doc enterprise-connectors/source-sap-hana"