Drop unsupported frameworks

Author: Metalnem

src/SharpFuzz.CommandLine/SharpFuzz.CommandLine.csproj

@@ -3,7 +3,7 @@
   <Import Project="..\..\build\Common.props" />
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp2.1;netcoreapp3.1;net5.0;net6.0;net7.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;net7.0;net8.0</TargetFrameworks>
     <OutputType>Exe</OutputType>
     <PackAsTool>true</PackAsTool>
     <ToolCommandName>sharpfuzz</ToolCommandName>