Stop using dashicons to show checked state of checkboxes

[EmpireOfLight]

Checkboxes should use the default system to indicate they are checked. (<input type="checkbox" checked> uses a dashicon check icon instead of the system's default check ui.

[EmpireOfLight]

Checkboxes use a checkmark dashicon, but they should just use the normal built in browser styling

[ocean90]

Context: ​https://wordpress.slack.com/archives/design-dashicons/p1474658281000116

[afercia]

Related: #35596

[adamsoucie]

Is the issue here that the browser's default is being replaced, or that the font color of the dashicon checkmark doesn't meet AA standards? The contrast ratio is 3.78, so if we're just worried about contrast here, darken the blue and we're done.

No need to decouple the dashicon system's that has been built on top of the browser default if all we have to do is improve the color a bit.

Update:
[WordPress Blue, 0073AA](​http://codepen.io/hugobaeta/full/RNOzoV/) fulfills our color contrast goal without swapping out the SVG implementation.

[EmpireOfLight]

The issue arose when testing svg replacement of the dashicons font in the admin, the checkbox and radios broke and would need to be re-coded (see ​https://make.wordpress.org/core/2016/10/23/converting-dashicons-to-svg/) . Rather than adding those to the list of fixes, it makes more sense to leave form rendering/chrome to the browser. The admin recently switched to system fonts, and similarly, removing the extra layer of styling might even be a performance boost.

[adamsoucie]

Works for me :)

@afercia, should we drop this one from the Color Contrast project as a result?

[afercia]

@adamsoucie if it gets merged, sure :) See #35596.

[afercia]

There are a few tickets now asking for form controls redesign, see #44749, #44606, and #35596.

[afercia]

Closing in favor of #47498 (5.3 blessed task). On current trunk, checkboxes use a SVG icon after [46248].

[SergeyBiryukov]

Duplicate of #47498.