Remove unnecessary Docker login from CleanAcrImagesCommand

[lbussell]

The cleanup command wrapped operations in ExecuteWithCredentialsAsync, which tried to Docker-login using the registry's service connection from publishConfig.RegistryAuthentication. That service connection was not referenced in the pipeline stage, causing Azure DevOps to refuse OIDC token issuance.

The Docker login was unnecessary - all ACR operations authenticate directly via cleanServiceConnection through the Azure SDK. Removing the wrapper and the unused IRegistryCredentialsProvider dependency should fix the pipeline failure.

Fixes #2028

[gdams]

This seems to have broken our cleanup pipeline now as the oras discover command still requires auth. That said I'm assuming that #2050 should resolve this issue @lbussell?

   at Microsoft.DotNet.ImageBuilder.Commands.CleanAcrImagesCommand.<>c__DisplayClass12_0.<<ProcessManifestsAsync>b__0>d.MoveNext() in /image-builder/ImageBuilder/Commands/CleanAcrImagesCommand.cs:line 168
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   at System.Threading.Tasks.Parallel.<>c__53`1.<<ForEachAsync>b__53_0>d.MoveNext()
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   at Microsoft.DotNet.ImageBuilder.Commands.CleanAcrImagesCommand.ProcessManifestsAsync(IAcrClient acrClient, IAcrContentClient acrContentClient, List`1 deletedImages, List`1 deletedRepos, ContainerRepository repository, Func`2 canDeleteManifest) in /image-builder/ImageBuilder/Commands/CleanAcrImagesCommand.cs:line 166
   at Microsoft.DotNet.ImageBuilder.Commands.CleanAcrImagesCommand.ProcessRepoAsync(IAcrClient acrClient, IAcrContentClient acrContentClient, ContainerRepository repository, List`1 deletedRepos, List`1 deletedImages) in /image-builder/ImageBuilder/Commands/CleanAcrImagesCommand.cs:line 96
   at Microsoft.DotNet.ImageBuilder.Commands.CleanAcrImagesCommand.ExecuteAsync() in /image-builder/ImageBuilder/Commands/CleanAcrImagesCommand.cs:line 81
   at System.CommandLine.Invocation.CommandHandler.GetResultCodeAsync(Object value, InvocationContext context)
   at System.CommandLine.Invocation.ModelBindingCommandHandler.InvokeAsync(InvocationContext context)
   at System.CommandLine.Invocation.InvocationPipeline.<>c__DisplayClass4_0.<<BuildInvocationChain>b__0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseParseErrorReporting>b__21_0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass19_0.<<UseMiddleware>b__0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass16_0.<<UseHelp>b__0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass25_0.<<UseVersionOption>b__0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass23_0.<<UseTypoCorrections>b__0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseSuggestDirective>b__22_0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseParseDirective>b__20_0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<UseDebugDirective>b__11_0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c.<<RegisterWithDotnetSuggest>b__10_0>d.MoveNext()
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   at System.CommandLine.Builder.CommandLineBuilderExtensions.<>c__DisplayClass14_0.<<UseExceptionHandler>b__0>d.MoveNext()