protobuf: bump to version 3.0.0

It also changes the python-protobuf.hash file to be a symbolic link to
../protobuf/protobuf.hash so that both hash files don't have to be
updated when protobuf is bumped.

In addition, the 0001-disable-unneeded-build-dependencies.patch patch
from package/python-protobuf/ is removed because it has been merged
upstream.

Signed-off-by: Jan Heylen <heyleke@gmail.com>
[Thomas: fix the build of python-protobuf.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>