Remove the repetitive warnings from the uapi headers.

Having

  WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS

every four lines made the headers harder to read, made the diffs much worse
each time we upgraded, and wasn't really providing any benefit. Before the
next uapi update, let's just stop doing this.

Bug: N/A
Test: builds, manually inspected files look right
Change-Id: Id7088cf750894c9d24950f3d53587fe3156c4f7d