Warnings in newly downloaded project. #4825

Why are there warnings in a newly created project?

1>C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin\Microsoft.Common.CurrentVersion.targets(2041,5): warning MSB3245: Could not resolve this reference. Could not locate the assembly "System.ComponentModel.DataAnnotations". Check to make sure the assembly exists on disk. If this reference is required by your code, you may get compilation errors. 8>C:\Users\markusbernhardt\Source\Repos\Acme.Test\aspnet-core\src\Acme.Test.Web.Core\Acme.Test.Web.Core.csproj : warning NU1603: Hangfire.Core 1.6.17 depends on Newtonsoft.Json (>= 5.0.0) but Newtonsoft.Json 5.0.0 was not found. An approximate best match of Newtonsoft.Json 5.0.1 was resolved. 9>Localization\LanguageAppService_Tests.cs(28,17,28,42): warning CS0162: Unreachable code detected 9>MultiTenantFactAttribute.cs(11,17,11,21): warning CS0162: Unreachable code detected 9>MultiTenantTheoryAttribute.cs(11,17,11,21): warning CS0162: Unreachable code detected 10>C:\Users\markusbernhardt\Source\Repos\Acme.Test\aspnet-core\src\Acme.Test.Web.Host\Acme.Test.Web.Host.csproj : warning NU1603: Hangfire.Core 1.6.17 depends on Newtonsoft.Json (>= 5.0.0) but Newtonsoft.Json 5.0.0 was not found. An approximate best match of Newtonsoft.Json 5.0.1 was resolved. 11>C:\Users\markusbernhardt\Source\Repos\Acme.Test\aspnet-core\src\Acme.Test.Web.Public\Acme.Test.Web.Public.csproj : warning NU1603: Hangfire.Core 1.6.17 depends on Newtonsoft.Json (>= 5.0.0) but Newtonsoft.Json 5.0.0 was not found. An approximate best match of Newtonsoft.Json 5.0.1 was resolved. 11>Startup\AuthConfigurer.cs(15,13,15,30): warning CS0618: 'BuilderExtensions.UseIdentity(IApplicationBuilder)' is obsolete: 'This method is obsolete and will be removed in a future version. The recommended alternative is UseAuthentication(). See <a class="postlink" href="https://go.microsoft.com/fwlink/?linkid=845470'">https://go.microsoft.com/fwlink/?linkid=845470'</a>