The “percentage” value is the mask value. ee.Image.updateMask will replace an image's mask wherever it is not exactly zero (= fully transparent). So:
var imageWithoutPartialMask = image.updateMask(1);
1 in this code is the new mask value; mask values are not actually stored as percentages but rather in the range
0.0 (transparent) to
Note that if you are planning to get aggregated data from a region (e.g. with
reduceRegion) this will cause the partial pixels at the edge to be over-weighted. Don't do this for images you're planning to do further computation on (unless you understand why the pixels are partially masked and know it doesn't matter or is correct for the situation); but for controlling the visualization it's fine.