Revert "scripts/Makefile.headersinst: install headers from scratch file"

This reverts commit 71f613a0. Upstream
has corrected the same bug with a different solution. Removing our
implementation to stay in sync with upstream. This is corrected in
upstream commit 3246a035.

Change-Id: I06fc01cfe30d3259e7e39d8e863312c3ff3b33e2
Signed-off-by: Ian Maund <imaund@codeaurora.org>