revert skills lib to not use a customized nuspec file to make its dependencies streamlined (#1966)

Author: lzc850612

lib/csharp/microsoft.bot.builder.skills/Microsoft.Bot.Builder.Skills/Microsoft.Bot.Builder.Skills.csproj

@@ -10,7 +10,7 @@
   <PropertyGroup>
     <TargetFramework>netstandard2.0</TargetFramework>
     <AssemblyName>Microsoft.Bot.Builder.Skills</AssemblyName>
-    <GeneratePackageOnBuild>false</GeneratePackageOnBuild>
+    <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
     <Company>Microsoft</Company>
     <Authors>Microsoft</Authors>
     <Description>Shared library for building Bot Framework Skills.</Description>
@@ -19,11 +19,8 @@
     <SignAssembly>true</SignAssembly>
     <DelaySign>true</DelaySign>
     <AssemblyOriginatorKeyFile>..\..\build\35MSSharedLib1024.snk</AssemblyOriginatorKeyFile>
-    <GeneratePackageOnBuild>false</GeneratePackageOnBuild>
+    <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
   </PropertyGroup>
-  <ItemGroup>
-    <Compile Remove="Models\SkillDefinition.cs"/>
-  </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.AspNetCore.Mvc.Core" Version="2.2.2"/>
     <PackageReference Include="Microsoft.Bot.Builder" Version="4.5.1"/>