For ubuntu 14.04 or earlier (e.g. indigo or jade), we should run
sudo apt-key del B01FA116
instead of
sudo apt-key del 421C365BD9FF1F717815A3895523BAEEB01FA116
since apt version is old.
B01FA116
is the last 8 characters of 421C365BD9FF1F717815A3895523BAEEB01FA116
.