Fix NETSDK1211 warning...

- EnableSingleFileAnalyzer is not supported for the target framework

Author: rvuistin

src/System.CommandLine/System.CommandLine.csproj

@@ -9,7 +9,6 @@
     <LangVersion>latest</LangVersion>
     <Description>Support for parsing command lines, supporting both POSIX and Windows conventions and shell-agnostic command line completions.</Description>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
-    <EnableSingleFileAnalyzer>true</EnableSingleFileAnalyzer>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(TargetFramework)' == '$(TargetFrameworkForNETSDK)'">