Clean out old pkgs refs

Rx.NET/Source/NuSpecs/Microsoft.Reactive.Testing.nuspec

@@ -17,7 +17,6 @@
         <dependencies>
             <dependency id="System.Reactive.Linq" version="$version$" />
             <dependency id="System.Reactive.PlatformServices" version="$version$" />
-            <dependency id="xunit" version="2.1.0" />
         </dependencies>
     </metadata>
     <files>

Rx.NET/Source/NuSpecs/System.Reactive.Core.nuspec

@@ -20,17 +20,9 @@
           </group>
           <group targetFramework="netstandard1.0">
             <dependency id="System.Reactive.Interfaces" version="$version$" />
-            <dependency id="System.ComponentModel" version="4.0.1-rc2-24027" />
-            <dependency id="System.Diagnostics.Contracts" version="4.0.1-rc2-24027" />
-            <dependency id="System.Dynamic.Runtime" version="4.0.11-rc2-24027" />
         </group>
         <group targetFramework="netcoreapp1.0">
             <dependency id="System.Reactive.Interfaces" version="$version$" />
-            <dependency id="System.ComponentModel" version="4.0.1-rc2-24027" />
-            <dependency id="System.Diagnostics.Contracts" version="4.0.1-rc2-24027" />
-            <dependency id="System.Dynamic.Runtime" version="4.0.11-rc2-24027" />
-            <dependency id="System.Threading.Thread" version="4.0.0-rc2-24027" />
-            <dependency id="System.Threading.ThreadPool" version="4.0.10-rc2-24027" />
         </group>
       </dependencies>
     </metadata>

Rx.NET/Source/NuSpecs/System.Reactive.Interfaces.nuspec

@@ -16,7 +16,6 @@
         <tags>Rx Reactive Extensions Observable LINQ Events</tags>
         <dependencies>
         <group targetFramework="netstandard1.0">
-          <dependency id="NETStandard.Library" version="1.5.0-rc2-24027" />
         </group>
       </dependencies>
     </metadata>

Rx.NET/Source/NuSpecs/System.Reactive.Linq.nuspec

@@ -22,7 +22,6 @@
           <group targetFramework="netstandard1.0">
             <dependency id="System.Reactive.Interfaces" version="$version$" />
             <dependency id="System.Reactive.Core" version="$version$" />
-            <dependency id="System.Runtime.InteropServices.WindowsRuntime" version="4.0.1-rc2-24027" />
           </group>
         </dependencies>
     </metadata>  

Rx.NET/Source/NuSpecs/System.Reactive.Providers.nuspec

@@ -20,8 +20,6 @@
           </group>
           <group targetFramework="netstandard1.0">
             <dependency id="System.Reactive" version="$version$" />
-            <dependency id="System.Linq.Queryable" version="4.0.1-rc2-24027" />
-            <dependency id="System.Reflection.Extensions" version="4.0.1-rc2-24027" />
           </group>
         </dependencies>
         <frameworkAssemblies>