Removed RuntimeFrameworkVersion values hardcoded into projects so that the...

Removed RuntimeFrameworkVersion values hardcoded into projects so that the newest (i.e. 2.1) runtime would be used, to get rid of "System.Runtime 4.2.1.0 file not found" errors when running integration tests.

src/CleanArchitecture.Infrastructure/CleanArchitecture.Infrastructure.csproj

 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <RuntimeFrameworkVersion>2.0.0</RuntimeFrameworkVersion>
     <TargetFramework>netcoreapp2.1</TargetFramework>
     <AssemblyName>CleanArchitecture.Infrastructure</AssemblyName>
     <PackageId>CleanArchitecture.Infrastructure</PackageId>

src/CleanArchitecture.Web/CleanArchitecture.Web.csproj

@@ -7,10 +7,6 @@
     <PackageId>CleanArchitecture.Web</PackageId>
   </PropertyGroup>
 
-  <PropertyGroup>
-    <RuntimeFrameworkVersion>2.0.0</RuntimeFrameworkVersion>
-  </PropertyGroup>
-  
   <ItemGroup>
     <Content Update="wwwroot\**\*;Views\**\*;Areas\**\Views;appsettings.json;web.config">
       <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>

tests/CleanArchitecture.Tests/CleanArchitecture.Tests.csproj

@@ -6,10 +6,6 @@
     <PreserveCompilationContext>true</PreserveCompilationContext>
   </PropertyGroup>
 
-  <PropertyGroup>
-    <RuntimeFrameworkVersion>2.0.0</RuntimeFrameworkVersion>
-  </PropertyGroup>
-
   <ItemGroup>
     <None Update="xunit.runner.json">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>