[udev] Remove udev defines as it is the only and default one

Since hal has been replaced and removed long ago, there is no reason
to keep udev separated. Makes code easier to read and eases Makefile
maintenance.

Signed-off-by: Philippe De Swert <philippe.deswert@jollamobile.com>
Merge pull request #17 from nemomobile/udev

[udev] Remove udev defines as it is the only and default one