Unused since commit f3f8f96842 ("tests: i2c_slave_spi: update to
proposed DT compatible naming").
Found with a script.
Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>
Port all users of 'set_conf_file' to use the built-in rules
instead. This follows the convention-over-configuration principle to
make the system as a whole simpler and more consistent.
Signed-off-by: Sebastian Bøe <sebastian.boe@nordicsemi.no>