[ci] revert changes to NuGet push to dotnet9 feed

[jonathanpeppers]

CI is failing with:

Response status code does not indicate success: 401 (Unauthorized).
Pushing Microsoft.Android.Ref.34.34.99.0-preview.5.290.nupkg to 'https://dnceng.pkgs.visualstudio.com/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/a54510f9-4b2c-4e69-b96a-6096683aaa1f/nuget/v2/'...
  PUT https://dnceng.pkgs.visualstudio.com/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/a54510f9-4b2c-4e69-b96a-6096683aaa1f/nuget/v2/
Using credentials from config. UserName: CustomToken
  Unauthorized https://dnceng.pkgs.visualstudio.com/9ee6d478-d288-47f7-aacc-f6e6d082ae6d/_packaging/a54510f9-4b2c-4e69-b96a-6096683aaa1f/nuget/v2/ 4958ms

• This reverts commit a0b7aad
• This reverts commit bbac9fe

@pjcollins will revisit these later.

We were trying to use a feature of darc/maestro, where it can manage pushing NuGet packages.

This will simplify the credentials to these feeds, when we get it working.

[jonathanpeppers]

Closing in favor of: #8964