Remove unneeded DESKTOP compilation symbol

Author: bording

LibGit2Sharp.Tests/LibGit2Sharp.Tests.csproj

@@ -2,7 +2,6 @@
 
   <PropertyGroup>
     <TargetFrameworks>net46;netcoreapp2.0</TargetFrameworks>
-    <DefineConstants Condition=" '$(TargetFramework)' == 'net46' ">$(DefineConstants);DESKTOP</DefineConstants>
   </PropertyGroup>
 
   <ItemGroup>

LibGit2Sharp.Tests/SetErrorFixture.cs

@@ -49,7 +49,7 @@ public void FormatAggregateException()
             Exception exceptionToThrow = new AggregateException(aggregateExceptionMessage, new Exception(innerExceptionMessage), new Exception(innerExceptionMessage2));
 
             StringBuilder sb = new StringBuilder();
-#if DESKTOP
+#if NETFRAMEWORK
             sb.AppendLine(aggregateExceptionMessage);
 #else
             sb.AppendLine($"{aggregateExceptionMessage} ({innerExceptionMessage}) ({innerExceptionMessage2})");