Revert "If the Nuget.config has already been generated, do not re-generate the file every time 'Run-Build' or 'Build' is called."

This reverts commit 9d5bd8637e.

build/NugetConfigFile.targets

@@ -1,11 +1,10 @@
 <Project ToolsVersion="15.0">
-  <Target Name="WriteNugetConfigFile"
-          Condition=" !Exists('$(GeneratedNuGetConfig)') ">
-
-    <ItemGroup>
-      <NugetConfigPrivateFeeds Include="$(ExternalRestoreSources.Split(';'))" />
-    </ItemGroup>
+  <Target Name="WriteNugetConfigFile">
 
+      <ItemGroup>
+        <NugetConfigPrivateFeeds Include="$(ExternalRestoreSources.Split(';'))" />
+      </ItemGroup>
+    
     <PropertyGroup>
       <NugetConfigHeader>
         <![CDATA[
@@ -41,13 +40,13 @@
 </configuration>
         ]]>
       </NugetConfigSuffix>
-
-    </PropertyGroup>
+    
+  </PropertyGroup>
 
     <WriteLinesToFile File="$(GeneratedNuGetConfig)"
                       Lines="$(NugetConfigHeader)"
                       Overwrite="true" />
-
+    
     <WriteLinesToFile Condition="'$(ExternalRestoreSources)' != '' and '$(DotNetBuildOffline)' != 'true'"
                       File="$(GeneratedNuGetConfig)"
                       Lines="&lt;add key=&quot;PrivateBlobFeed&quot; value=&quot;%(NugetConfigPrivateFeeds.Identity)&quot; /&gt;"