To hide just the labels, in version 2.3.0 of Charts.js, you disable ticks like so:

options: {
    scales: {
        yAxes: [{
            ticks: {
                display: false
            }
        }]
    }
}

For version 2, you can do this with the Scales option in the global configuration.

  var ctx = document.getElementById("log");
  var chart = new Chart(ctx, {
      type: 'line',
      options: {
        scales: {
          xAxes: [{
            display: false
          }],
          yAxes: [{
            display: false
          }],
        }
      },
      data: {
        labels: ['Item 1', 'Item 2', 'Item 3'],
        datasets: [{
            fill: false,
            borderWidth: 1,
            data: [10, 20, 30]
        }]
      }
    });

This will hide labels in Y-Axis: (but not X-Axis)

    scaleShowLabels: false,