OWIN: Remove Microsoft.AspNet.WebApi.HelpPage dependency (#2416)

The package auto copies a lot of unnecessary files to the
target project, and cannot be removed while Microsoft.Identity.Web
.OWIN is installed.

Author: Strepto

src/Microsoft.Identity.Web.OWIN/Microsoft.Identity.Web.OWIN.csproj

@@ -25,7 +25,6 @@
     <PackageReference Include="Microsoft.AspNet.Mvc" Version="5.2.7" />
     <PackageReference Include="Microsoft.AspNet.Web.Optimization" Version="1.1.3" />
     <PackageReference Include="Microsoft.AspNet.WebApi" Version="5.2.7" />
-    <PackageReference Include="Microsoft.AspNet.WebApi.HelpPage" Version="5.2.7" />
     <PackageReference Include="Microsoft.IdentityModel.Protocols.WsFederation" Version="5.5.0" />
     <PackageReference Include="Microsoft.Owin.Host.SystemWeb" Version="4.2.2" />
     <PackageReference Include="Microsoft.Owin.Security.ActiveDirectory" Version="4.2.2" />