Remove Newtonsoft reference form core.test

Author: peombwa

tests/Microsoft.Graph.Core.Test/Microsoft.Graph.Core.Test.csproj

@@ -118,9 +118,6 @@
     <PackageReference Include="MSTest.TestFramework">
       <Version>1.4.0</Version>
     </PackageReference>
-    <PackageReference Include="Newtonsoft.Json">
-      <Version>11.0.2</Version>
-    </PackageReference>
   </ItemGroup>
   <Choose>
     <When Condition="'$(VisualStudioVersion)' == '10.0' And '$(IsCodedUITest)' == 'True'">