Paste this code into the 'Remotes' tab in the Script editor (alt+r), edit the #CHANNEL with your channel that you want to not display any join/part/quit message.

Code:
ON !^*:JOIN:#CHANNEL: { haltdef }
ON !^*:PART:#CHANNEL: { haltdef }
ON !^*:QUIT: {
  var %ch = #CHANNEL
  var %t = $chan(0)
  if (!%t) { return }
  var %i = 1
  while (%i <= %t) {
    var %c = $chan(%i)
    if (%c == %ch) && ($nick ison %c) { haltdef }
    elseif (%c !== %ch) && ($nick ison %c) { echo -tc quit %c * Quits: $nick ( $+ $iif($address($nick,10),$mid($v1,3-),N/A) $+ ) ( $+ $1- $+ ) }
    inc %i
  }
}