SmartRTL mode disappeared

#### Issue details
Sorry if it has already been reported but I could not find a related issue : the latest Mission Planner version (1.3.58 was OK, 1.3.62 is not OK) sometimes does not seem to evoke any more the SmartRTL mode (e.g. not in Set Mode button list, FS_THR_ENABLE param description and probably elsewhere). I found also other people talking about it on [https://discuss.ardupilot.org/t/copter-3-6-2-released/35476/16](https://discuss.ardupilot.org/t/copter-3-6-2-released/35476/16).

#### Version
1.3.62

#### Platform
[ ] All
[ ] AntennaTracker
[x] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
Quadrotor

#### Hardware type
HKPilot32 with ChibiOS and Copter V3.6.4 (6c4da9e3), SITL with Copter V3.7.0-dev (5f9de3cf)

#### Logs
N/A

Start by reproducing the missing SmartRTL mode in Mission Planner 1.3.62 with Copter, comparing it against 1.3.58 and the listed hardware or SITL environments. Check the Set Mode list and FS_THR_ENABLE parameter description; the issue is done when SmartRTL appears consistently in the affected views.

Written by the indexing model from the issue text.