ppp: remove erroneous generated header from the source tree

ppp: remove erroneous generated header from the source tree

ppp-2.5.2 tarball ships a generated header with various
configuration settigns that takes precedence over the same
header generated into the build directory during the actual build.

This resulted in various linking fails that were worked around
by enabling multilink in 2.5.2 version update. The correct fix
that removes all contamination is to remove the bogus header first.

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>