[Data Factory] Remove unnecessary additional property for data flow entity

[jackmagic313]

Latest improvements:

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[openapi-sdkautomation]

In Testing, Please Ignore

[Logs] (Generated from 1cac622, Iteration 2)

.NET: test-repo-billy/azure-sdk-for-net [Logs] [Diff]

• Microsoft.Azure.Management.DataFactory [Logs] [Instructions] [Generation PR]
  • Microsoft.Azure.Management.DataFactory.4.1.3.nupkg
  • Microsoft.Azure.Management.DataFactory.4.1.3.snupkg

Python: test-repo-billy/azure-sdk-for-python [Logs] [Diff]

• azure-mgmt-datafactory [Logs] [Instructions] [Generation PR]
  • azure-mgmt-datafactory-0.8.0.zip
  • azure_mgmt_datafactory-0.8.0-py2.py3-none-any.whl

Java: test-repo-billy/azure-sdk-for-java [Logs] [Diff]

• datafactory/resource-manager/v2017_09_01_preview [Logs] [Generation PR]
• datafactory/resource-manager/v2018_06_01 [Logs]

Go: test-repo-billy/azure-sdk-for-go [Logs] [Diff]

• datafactory/mgmt/2018-06-01 [Logs]
• preview/datafactory/mgmt/2017-09-01-preview [Logs]

JavaScript: test-repo-billy/azure-sdk-for-js [Logs] [Diff]

• @azure/arm-datafactory [Logs] [Instructions]
  • azure-arm-datafactory-5.3.0.tgz

[AutorestCI]

Automation for azure-sdk-for-python

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-python#7315

[azuresdkci]

Can one of the admins verify this patch?

[AutorestCI]

Automation for azure-sdk-for-go

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-go#5865

[anuchandy]

Discussed with @jackmagic313, this continuation of the PR #7088, where we identified that additional properties are not allowed in polymorphic types. Merging this.