MC LandDetector: remove dependency on MPC_LAND_SPEED and MPC_LAND_CRWL

Don't consider these params for vertical speed threshold,
and instead increase the default for LNDMC_Z_VEL_MAX and
use solely that one. Makes the land detector outcome more
predictable and its interal logic simpler, while the new
default tuning is resulting in about the same vz threshold
as before.

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/mc_pos_control/mc_pos_control_params.c

@@ -448,8 +448,9 @@ PARAM_DEFINE_FLOAT(MPC_TILTMAX_LND, 12.0f);
 PARAM_DEFINE_FLOAT(MPC_LAND_SPEED, 0.7f);
 
 /**
- * Land crawl descend rate. Used below MPC_LAND_ALT3 if distance
- * sensor data is availabe.
+ * Land crawl descend rate
+ *
+ * Used below MPC_LAND_ALT3 if distance sensor data is availabe.
  *
  * @unit m/s
  * @min 0.1