Merge pull request #827 from microsoft/fix/removesystemjsontextref

Remove unnecessary reference that made netcoreapp2.1 incompatible

Author: darrelmiller

src/Microsoft.OpenApi/Microsoft.OpenApi.csproj

@@ -38,7 +38,6 @@
 
     <ItemGroup>
         <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
-        <PackageReference Include="System.Text.Json" Version="6.0.2" />
     </ItemGroup>
 
     <ItemGroup>