fix: sharpen blurry checkmark icon (#1487)

`image(with)` is currently buggy and returns an image with the wrong scale (causing it to be blurry).  Remove this call, it is actually unnecessary because `tintColor` does the same thing.

Source/CourseOutlineItemView.swift

@@ -185,7 +185,7 @@ public class CourseOutlineItemView: UIView {
 
     func setContentIcon(icon: Icon?, color: UIColor) {
         shouldShowLeadingView = true
-        let image = icon?.imageWithFontSize(size: SmallIconSize).image(with: color)
+        let image = icon?.imageWithFontSize(size: SmallIconSize)
         leadingImageButton.setImage(image, for: .normal)
         leadingImageButton.tintColor = color
         if let accessibilityText = icon?.accessibilityText {