Unset _I3_RESTART_FD after restart (#3775)
Unset _I3_RESTART_FD after restart (#3775)

Closes #3764
Closes #3765
i3/i3,i3/i3,i3/i3,Airblader/i3,Airblader/i3-original,stapelberg/i3,stapelberg/i3,Airblader/i3-original,Airblader/i3,Airblader/i3-original,stapelberg/i3,Airblader/i3-original,Airblader/i3,Airblader/i3,i3/i3,stapelberg/i3,Airblader/i3-original