Remove netcoreapp2.0 test TFMs (dotnet/extensions#907)

.NET Core 2.0 reached EOL last year. This removes multi-targeting our test projects and test assets to only use .NET Core 2.1 and .NET Framework 4.6.1.\n\nCommit migrated from dotnet/extensions@084494d

Author: natemcmaster

src/Caching/Memory/test/Microsoft.Extensions.Caching.Memory.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(StandardTestTfms)</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1;net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>

src/Caching/Redis/test/Microsoft.Extensions.Caching.Redis.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(StandardTestTfms)</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1;net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>

src/Caching/SqlServer/test/Microsoft.Extensions.Caching.SqlServer.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(StandardTestTfms)</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1;net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>

src/HttpClientFactory/Http/test/Microsoft.Extensions.Http.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(StandardTestTfms)</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1;net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>

src/HttpClientFactory/Polly/test/Microsoft.Extensions.Http.Polly.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(StandardTestTfms)</TargetFrameworks>
+    <TargetFrameworks>netcoreapp2.1;net461</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>