[release/3.0] Switch to embedded package icon

[wtgodbe]

Contributes to https://github.com/aspnet/AspNetCore-Internal/issues/3103

@Pilchie does this need to go through ask mode?

[wtgodbe]

Just updated to the GA SDK

[wtgodbe]

On Linux:

F:\workspace.1_work\1\s.dotnet\sdk\3.0.100\Sdks\NuGet.Build.Tasks.Pack\build\NuGet.Build.Tasks.Pack.targets(198,5): error NU5128: Some target frameworks declared in the dependencies group of the nuspec and the lib/ref folder do not have exact matches in the other location. Consult the list of actions below: [F:\workspace.1_work\1\s\src\dotnet-ef\dotnet-ef.csproj]
F:\workspace.1_work\1\s.dotnet\sdk\3.0.100\Sdks\NuGet.Build.Tasks.Pack\build\NuGet.Build.Tasks.Pack.targets(198,5): error NU5128: - Add lib or ref assemblies for the netcoreapp2.1 target framework [F:\workspace.1_work\1\s\src\dotnet-ef\dotnet-ef.csproj]

[dougbu]

@wtgodbe probably needs a _._ file in the .nupkg

[wtgodbe]

Don't merge until #18032 is in

[dougbu]

@wtgodbe is this good to go? It's blocking #18043 and #18032 no longer blocks it.