message: Don't show a reason if there's no reason for a kick/ban
  Fixes
diff: @@ -305,7 +305,7 @@ module.exports = React.createClass({
  const {memberName, reason} = this._getKickOrBanInfo();
  title = _t("You were kicked from %(roomName)s by %(memberName)s",
  {memberName, roomName: this._roomName()});
  - subTitle = _t("Reason: %(reason)s", {reason});
  + subTitle = reason ? _t("Reason: %(reason)s", {reason}) : null;
  if (this._joinRule() === "invite") {
  primaryActionLabel = _t("Forget this room");
  @@ -322,7 +322,7 @@ module.exports = React.createClass({
  const {memberName, reason} = this._getKickOrBanInfo();
  title = _t("You were banned from %(roomName)s by %(memberName)s",
  {memberName, roomName: this._roomName()});
  - subTitle = _t("Reason: %(reason)s", {reason});
  + subTitle = reason ? _t("Reason: %(reason)s", {reason}) : null;
  primaryActionLabel = _t("Forget this room");
  primaryActionHandler = this.props.onForgetClick;
  break;
  