linux: drop LDFLAGS override

The current linux code overrides LDFLAGS that the kernel itself might be
setting up. Looking at the history, there doesn't seem to be any reason
for this override. It was added in ea8b1fa6 without any logic.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>