removeUnusedLayerStyles.js

function cleanLayerStyless(array) {
  var layers = []
  array.forEach(function(layer) {
    if (layer.class() == 'MSShapeGroup') layers.push(layer)
  })

  for (var i = 0; i < layers.length; i++) {
    layers.forEach(function(layer, index) {
      var fills = layer.style().fills()
      fills.forEach(function(fill, fillIndex) {
        log(layer.name())
        if (fill.isEnabled() == 0) {
          log(fillIndex)
          log(fill)
          layer.style().removeStyleFillAtIndex(fillIndex)
        }
      })
    })
  }
}


function deleteUnusedStyles(context, dialog) {
    if (dialog == undefined) dialog = false
    var doc = context.document

    var selection = context.selection
    var layers = doc.currentPage().children()
    var layerGroups = []

    layers.forEach(function(layer) {
        if (layer.className() == 'MSShapeGroup') {
            layerGroups.push(layer)
        }
    })

    if (!dialog) {
        cleanLayerStyless(selection)
        doc.showMessage("All selected layers have been cleaned")
    } else {
        cleanLayerStyless(layers)
        doc.showMessage("All the layers have been cleaned")
    }
}
deleteUnusedStyles(context, true)