Copter: RTL does not descend to clear vertical fence breach

#### Issue details
Line 541 of mode_rtl.cpp prevents the vehicle from descending below the altitude fence if RTL is triggered as the fence breach behaviour. This is clearly intended functionality from lines 522 through 538

Removing line 541 will fix the problem

#### Version
master

#### Platform
[ ] All
[ ] AntennaTracker
[X] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

#### Airframe type
all

#### Hardware type
all

#### Logs
N/A

Open mode_rtl.cpp and inspect line 541 alongside lines 522–538, which describe the intended fence-breach RTL behavior. Verify how the altitude-fence check prevents descent, then confirm that RTL can descend below the fence to clear the breach without affecting other RTL behavior. The issue identifies removing line 541 as the proposed fix; logs are not available.

Written by the indexing model from the issue text.