Enable protobuf provisioning for all linux platforms, since it's
required to build qtbase with protobuf support.
Delete install_protobuff for macos 10.14 since it's not used and
wouldn't build without special casing.
Change-Id: I9c7dea876c45dbcbfc3110b106ae683bbe9179ec
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>