remove netstandard.library ref

Ix.NET/Source/NuSpecs/System.Interactive.Async.nuspec

@@ -19,7 +19,6 @@
     </frameworkAssemblies>
     <dependencies>
       <group targetFramework="netstandard1.0">
-        <dependency id="NETStandard.Library" version="1.5.0-rc2-24027" />
         <dependency id="System.Collections" version="4.0.11-rc2-24027" />
         <dependency id="System.Diagnostics.Debug" version="4.0.11-rc2-24027" />
         <dependency id="System.Linq" version="4.1.0-rc2-24027" />

Ix.NET/Source/NuSpecs/System.Interactive.nuspec

@@ -21,7 +21,6 @@
     </frameworkAssemblies>
     <dependencies>
       <group targetFramework="netstandard1.0">
-        <dependency id="NETStandard.Library" version="1.5.0-rc2-24027" />
         <dependency id="System.Collections" version="4.0.11-rc2-24027" />
         <dependency id="System.Diagnostics.Debug" version="4.0.11-rc2-24027" />
         <dependency id="System.Linq" version="4.1.0-rc2-24027" />