main/*: move udev rules to usr-merge
Besides eudev itself which !72703 (merged) takes care off, only main/btrfs-progs and main/openobex are left. They determine the directory to install the rules to by running pkgconf udev --variable=udevdir (although for openobex this can be overwriten by a CMake line) which afaik should return the usr-merge directory after !72703 (merged) is merged.
Edited by Bart Ribbers