arm, remove special handling for ARM types

[XiaofeiCao]

typespec-azure-resource-manager has fixed the naming issue: Azure/typespec-azure#762
Our special handling for Resource, ProxyResource and ArmResource is no longer needed.

[XiaofeiCao]

This deduplication logic is due to same dummy resource schema being added many times here:
https://github.com/Azure/autorest.java/pull/2749/files#diff-14fdfb2e0df46da414f4d04a218f03e4e5f2737d3a9672b9c4e4feb16419445eL2160

[weidongxu-microsoft]

ArmResource is deprecated but not removed. Do we still need this till it get removed?

[XiaofeiCao]

ArmResource is deprecated but not removed. Do we still need this till it get removed?

I searched current specs repo, seems (Arm)Resource is only used in template parameters as : https://github.com/search?q=repo%3AAzure%2Fazure-rest-api-specs+%22ArmResource%22&type=code&p=1
I added back one ArmResource in our test, seems ok.

(Arm)Resource is used as base model for all Tracked/Proxy/ExtensionResource(Base). I guess service is not allowed to let its models directly extend ArmResource, otherwise it'll break JS and Python..

[XiaofeiCao]

Offline sync with Chenjie, service will not use ArmResource for green field. For brownfields, there exists cases where model directly extends Resource, and will be converted to Resource in tsp, still no ArmResource. And existing ArmResource will be fixed to Resource.