Prevent prebuilts from ending up in the sharedframework

--- a/src/pkg/packaging-tools/framework.sharedfx.props
+++ b/src/pkg/packaging-tools/framework.sharedfx.props
@@ -26,8 +26,6 @@
     <RestoreAllBuildRids>false</RestoreAllBuildRids>
     <!-- Ensure only this repo's NuGet.config file is used. -->
     <RestoreConfigFile>$(ProjectDir)NuGet.config</RestoreConfigFile>
-    <!-- Use repo-restored packages for platforms and targets dependencies -->
-    <RestoreFallbackFolders>$(PackagesDir)</RestoreFallbackFolders>
     <!-- Don't error due to lack of runtime-specific deps, we're referencing those directly -->
     <EnsureRuntimePackageDependencies>false</EnsureRuntimePackageDependencies>
     <!-- Use a project-local packages folder. 'p', not 'packages': max path breathing room. -->