remove packageReference from project file for management sdk

[chunyu3]

Description

Fix #4913

Problem-tp-solve: Duplicate compile items
When generate a new service from typespec, the .NET codegen will generate scaffolding (include project file) for this new SDK. In the generated project file it includes several packageReference to add compile dependency. But in azure-sdk-for-net, the engsys already include all depended packages for management-plane SDK in Directory.Build.Common.targets. So the build will fail because of duplicate compile items.

Solution:
Since existing SDKs in azure-sdk-for-net contain define those packageRefernce in each SDK's project file, and we also need to support management SDKs from swagger which use the dotnet templates to create scaffolding folder, we decide to change in codegen side to remove packageReference when create scaffolding which will keep consistent with current SDKs.

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