CLEANUP: wurfl: make use of the late init registration

CLEANUP: wurfl: make use of the late init registration

This removes some #ifdefs from the main haproxy code path and enables
error checking. The current code only makes use of warnings even for
some errors that look serious. While this choice is questionnable, it
has been kept as-is, and only the return codes were adapted to ERR_WARN
to at least report that some warnings were emitted. ha_wurfl_init() was
unexported as it's not needed anymore.