Move TargetFramework properties into projects

They cause more confusion and issues being imported than its worth.

src/Directory.Build.props

@@ -1,7 +1,3 @@
 <Project>
   <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory)../, Directory.Build.props))\Directory.Build.props" Condition=" '$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory)../, Directory.Build.props))' != '' " />
-
-  <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
-  </PropertyGroup>
 </Project>

src/Library/Library.csproj

@@ -1,3 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
-
+  <PropertyGroup>
+    <TargetFramework>netstandard2.0</TargetFramework>
+  </PropertyGroup>
 </Project>

test/Directory.Build.props

@@ -2,7 +2,6 @@
   <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory)../, Directory.Build.props))\Directory.Build.props" Condition=" '$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory)../, Directory.Build.props))' != '' " />
 
   <PropertyGroup>
-    <TargetFrameworks>net5.0;netcoreapp3.1;net472</TargetFrameworks>
     <IsPackable>false</IsPackable>
     <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
   </PropertyGroup>

test/Library.Tests/Library.Tests.csproj

@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
+    <TargetFrameworks>net5.0;netcoreapp3.1;net472</TargetFrameworks>
     <RootNamespace />
   </PropertyGroup>