Remove IntegratedShell InstallationTarget

Author: jcansdale

src/GitHub.VisualStudio.Vsix/source.extension.vsixmanifest

@@ -14,7 +14,6 @@
   </Metadata>
   <Installation AllUsers="true" Experimental="false">
     <InstallationTarget Id="Microsoft.VisualStudio.Community" Version="[14.0,17.0)" />
-    <InstallationTarget Id="Microsoft.VisualStudio.IntegratedShell" Version="[15.0,17.0)" />
   </Installation>
   <Dependencies>
     <Dependency Id="Microsoft.Framework.NDP" DisplayName="Microsoft .NET Framework" d:Source="Manual" Version="[4.5,)" />