Fix System.Xml.XPath.XmlDocument tests conflict

These were failing to build because the referenced an older version of
Xml.XPath then the library.  This was due to the library using a project
reference instead of a package reference.

Author: ericstj

src/System.Xml.XPath.XmlDocument/src/System.Xml.XPath.XmlDocument.csproj

@@ -87,11 +87,5 @@
   <ItemGroup>
     <None Include="project.json" />
   </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="..\..\System.Xml.XPath\src\System.Xml.XPath.csproj">
-      <Project>{be28323e-327a-4e0f-b7f9-16ab7eab59dd}</Project>
-      <Name>System.Xml.XPath</Name>
-    </ProjectReference>
-  </ItemGroup>
   <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.targets))\dir.targets" />
 </Project>

src/System.Xml.XPath.XmlDocument/src/project.json

@@ -11,7 +11,8 @@
     "System.Runtime.Extensions": "4.0.10",
     "System.Threading": "4.0.10",
     "System.Xml.ReaderWriter": "4.0.10",
-    "System.Xml.XmlDocument": "4.0.0"
+    "System.Xml.XmlDocument": "4.0.0",
+    "System.Xml.XPath": "4.0.0"
   },
   "frameworks": {
     "dnxcore50": {}

src/System.Xml.XPath.XmlDocument/src/project.lock.json

@@ -300,6 +300,25 @@
         "runtime": {
           "lib/dotnet/System.Xml.XmlDocument.dll": {}
         }
+      },
+      "System.Xml.XPath/4.0.0": {
+        "dependencies": {
+          "System.Runtime": "4.0.20",
+          "System.IO": "4.0.10",
+          "System.Xml.ReaderWriter": "4.0.10",
+          "System.Resources.ResourceManager": "4.0.0",
+          "System.Collections": "4.0.10",
+          "System.Globalization": "4.0.10",
+          "System.Diagnostics.Debug": "4.0.10",
+          "System.Runtime.Extensions": "4.0.10",
+          "System.Threading": "4.0.10"
+        },
+        "compile": {
+          "ref/dotnet/System.Xml.XPath.dll": {}
+        },
+        "runtime": {
+          "lib/dotnet/System.Xml.XPath.dll": {}
+        }
       }
     }
   },
@@ -1021,6 +1040,37 @@
         "ref/xamarinios10/_._",
         "ref/xamarinmac20/_._"
       ]
+    },
+    "System.Xml.XPath/4.0.0": {
+      "serviceable": true,
+      "sha512": "jalVwhZSwErcW28NZOE3Dqb6B1XA4DAsL15JvykYIKXtXYQU8PI5GXssjF5G0bLm8/6Gko2e1SOjRs/MoeAKrw==",
+      "files": [
+        "System.Xml.XPath.4.0.0.nupkg",
+        "System.Xml.XPath.4.0.0.nupkg.sha512",
+        "System.Xml.XPath.nuspec",
+        "lib/dotnet/System.Xml.XPath.dll",
+        "lib/MonoAndroid10/_._",
+        "lib/MonoTouch10/_._",
+        "lib/net46/System.Xml.XPath.dll",
+        "lib/xamarinios10/_._",
+        "lib/xamarinmac20/_._",
+        "ref/dotnet/System.Xml.XPath.dll",
+        "ref/dotnet/System.Xml.XPath.xml",
+        "ref/dotnet/de/System.Xml.XPath.xml",
+        "ref/dotnet/es/System.Xml.XPath.xml",
+        "ref/dotnet/fr/System.Xml.XPath.xml",
+        "ref/dotnet/it/System.Xml.XPath.xml",
+        "ref/dotnet/ja/System.Xml.XPath.xml",
+        "ref/dotnet/ko/System.Xml.XPath.xml",
+        "ref/dotnet/ru/System.Xml.XPath.xml",
+        "ref/dotnet/zh-hans/System.Xml.XPath.xml",
+        "ref/dotnet/zh-hant/System.Xml.XPath.xml",
+        "ref/MonoAndroid10/_._",
+        "ref/MonoTouch10/_._",
+        "ref/net46/System.Xml.XPath.dll",
+        "ref/xamarinios10/_._",
+        "ref/xamarinmac20/_._"
+      ]
     }
   },
   "projectFileDependencyGroups": {
@@ -1036,7 +1086,8 @@
       "System.Runtime.Extensions >= 4.0.10",
       "System.Threading >= 4.0.10",
       "System.Xml.ReaderWriter >= 4.0.10",
-      "System.Xml.XmlDocument >= 4.0.0"
+      "System.Xml.XmlDocument >= 4.0.0",
+      "System.Xml.XPath >= 4.0.0"
     ],
     "DNXCore,Version=v5.0": []
   }