Disable sv_gameplayfix_unstickplayers as it introduces glitchy visuals while riding elevators

Prior to the introduction of sv_gameplayfix_unstickplayers 2 in the QC physics, this option was disabled. The new option was introduced in an attempt to fix glitchy views when dying while noclipping out of bounds (unsure if this is still reproducible), but it caused a side effect where the view became incredibly choppy while riding elevators.
This change restores the old value of 0.
Closes #2740