Remove the utils_resolve_relative function that is not useful anymore

As all of the work is now done in utils_partial_realpath and
utils_expand_path, utils_resolve_relative is not necessary
anymore and should be deleted from the sources.

Signed-off-by: Raphaël Beamonte <raphael.beamonte@gmail.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>