It appears that we can turn off the default “All Apps” view in the new windows 10 start menu with the policy at:
User Config – Policies – Administrative Template – Start Menu and Task bar –
Remove All Programs list from the Start menu

It appears that you can “remove” the default list and keep only the specific items you pin there.

Specifically the helpful group policy wording is:

“This policy setting allows you to remove the All Programs list from the Start menu.

If you enable this policy setting, the “All Programs” item is removed from the simple Start menu. The Start Screen will show the All Apps view, but it will only contain items that are pinned to start.

If you disable or do not configure this policy setting, the “All Programs” item remains on the simple Start menu.”

I found this on the longer list of Windows 10 Start Menu policies at:
https://technet.microsoft.com/en-us/library/mt484191%28v=vs.85%29.aspx