Fix test project build warnings about dependency conflicts

Several project.json files were still referencing the old xunit assemblies, causing such warnings during build.  Another had inconsistent versions of dependent libraries.

Author: stephentoub

src/System.Net.Primitives/tests/PalTests/project.json

@@ -1,30 +1,27 @@
 {
   "dependencies": {
-    "System.Collections": "4.0.0",
+    "Microsoft.Win32.Primitives": "4.0.0",
+    "System.Collections": "4.0.10",
+    "System.Collections.NonGeneric": "4.0.0",
+    "System.ComponentModel.EventBasedAsync": "4.0.10",
     "System.Console": "4.0.0-beta-*",
     "System.Diagnostics.Contracts": "4.0.0",
+    "System.Diagnostics.Debug": "4.0.10",
     "System.Diagnostics.Tracing": "4.0.20",
-    "System.Runtime": "4.0.20",
-    "System.Runtime.Extensions": "4.0.10",
-    "System.Resources.ResourceManager": "4.0.0",
-    "System.Threading": "4.0.0",
-    "System.Threading.Tasks": "4.0.0",
-    "System.Runtime.InteropServices": "4.0.20",
-    "System.Runtime.Handles": "4.0.0",
+    "System.Globalization": "4.0.10",
     "System.IO": "4.0.10",
     "System.IO.FileSystem": "4.0.0",
     "System.IO.FileSystem.Primitives": "4.0.0",
-    "System.ComponentModel.EventBasedAsync": "4.0.10",
-    "System.Globalization": "4.0.0",
-    "System.Diagnostics.Debug": "4.0.10",
-    "System.Collections.NonGeneric": "4.0.0",
+    "System.Resources.ResourceManager": "4.0.0",
+    "System.Runtime": "4.0.20",
+    "System.Runtime.Extensions": "4.0.10",
+    "System.Runtime.Handles": "4.0.0",
+    "System.Runtime.InteropServices": "4.0.20",
     "System.Security.Claims": "4.0.0",
     "System.Security.SecureString": "4.0.0-beta-*",
-    "Microsoft.Win32.Primitives": "4.0.0",
-    "xunit": "2.0.0-beta5-build2785",
-    "xunit.abstractions.netcore": "1.0.0-prerelease",
-    "xunit.assert": "2.0.0-beta5-build2785",
-    "xunit.core.netcore": "1.0.1-prerelease",
+    "System.Threading": "4.0.10",
+    "System.Threading.Tasks": "4.0.0",
+    "xunit": "2.1.0-beta3-*",
     "xunit.netcore.extensions": "1.0.0-prerelease-*"
   },
   "frameworks": {