ttcn3-bts: Update cfg for test TC_tx_power_start_ramp_up_bcch
The test mentioned above is added in osmo-ttcn3-hacks.git Ieb7444c6312bbeab64da2732393b3facf3e1f003.
config files are updated to make sense: * "nominal power" in osmo-bsc.cfg reflects correct default nominal tx power of fake_trx. * "osmotrx tx-attenuation" in osmo-bts.cfg is removed to let osmo-bts use the value received through OML (max_power_red 20). * "power-ramp step-size" in osmo-bts.cfg is increased to speed up the test. There's no good reason to keep it lower.
