Remove XML documentation output in test project. It causes errors to show up

in ReSharper.

src/ProtocolBuffers.Test/ProtocolBuffers.Test.csproj

@@ -45,7 +45,8 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <CodeAnalysisRuleSet>AllRules.ruleset</CodeAnalysisRuleSet>
-    <DocumentationFile>bin\Debug\Google.ProtocolBuffers.Test.XML</DocumentationFile>
+    <DocumentationFile>
+    </DocumentationFile>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <NoWarn>1591</NoWarn>
   </PropertyGroup>
@@ -57,7 +58,8 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <CodeAnalysisRuleSet>AllRules.ruleset</CodeAnalysisRuleSet>
-    <DocumentationFile>bin\Release\Google.ProtocolBuffers.Test.XML</DocumentationFile>
+    <DocumentationFile>
+    </DocumentationFile>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <NoWarn>1591</NoWarn>
   </PropertyGroup>