Fix issues with feeds used to restore testapps

* Remove duplicated feeds from testapps/NuGet.config
* Don't specify feeds as part of restore. Let testapps/NuGet.config dictate this.
* Switch to dotnet.myget.org

NuGet.config

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <packageSources>
-    <add key="AspNetVNext" value="https://www.myget.org/F/aspnetcidev/api/v3/index.json" />
+    <add key="AspNetCore" value="https://dotnet.myget.org/F/aspnetcore-ci-dev/api/v3/index.json" />
     <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>

test/Microsoft.AspNetCore.Mvc.Razor.Precompilation.Tests/Infrastructure/ApplicationTestFixture.cs

@@ -91,10 +91,6 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Precompilation
             var args = new[]
             {
                 Path.Combine(applicationDirectory, "project.json"),
-                "-s",
-                packagesDirectory,
-                "-s",
-                ApplicationPaths.ArtifactPackagesDirectory,
                 "--packages",
                 TempRestoreDirectory,
             };

testapps/NuGet.config

@@ -1,8 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
   <packageSources>
-    <add key="AspNetVNext" value="https://www.myget.org/F/aspnetcidev/api/v3/index.json" />
-    <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
     <add key="LocalArtifacts" value="../artifacts/build" />
   </packageSources>
 </configuration>