Remove packages.props reference

Remove reference to packages.props that isn't used with the migration to use Arcade for compilation.

Author: martincostello

generators/app/templates/Project.csproj

@@ -1,7 +1,5 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
-  <Import Project="..\..\build\packages.props" />
-
   <PropertyGroup>
     <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>