Since it's being added when we install the headers anyway,
we might as well get rid of it. If anything, we should point
coders to the COPYING file in the project's root directory
instead of duplicating the same (large-ish) text everywhere.

Signed-off-by: Andreas Ericsson <ae@op5.se>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>