Remove duplicate dependency

Author: Cory Thompson

build/package/WebPush.nuspec

@@ -14,7 +14,6 @@
     <dependencies>
        <dependency id="BouncyCastle" version="1.8.1"/>
        <dependency id="Newtonsoft.Json" version="6.0.1"/>
-       <dependency id="Microsoft.Net.Http" version="2.2.29"/>
        <dependency id="Microsoft.Bcl" version="1.1.10" />
        <dependency id="Microsoft.Bcl.Async" version="1.0.168" />
        <dependency id="Microsoft.Bcl.Build" version="1.0.14" />