[Bug] Deleted Element Styles Are Still Saved

Expected Behavior: After deleting an element from the canvas that has received custom styles using the style manager, the deleted element's styles should no longer be saved in the styles JSON.

Actual Behavior: The styles JSON retains entries for deleted elements on save.

Steps to Reproduce:

1. Fiddle based on the starter template that logs the styles JSON to the console on save is available at: https://jsfiddle.net/g48sLxrt/
2. Modify the default text block, changing its color to red using the style manager. The following appears in the console:

[{"selectors":[{"name":"c620","label":"c620","type":1,"active":true,"private":false,"protected":false}],"style":{"padding":"25px","color":"red"}}]

3. Delete the existing, styled text block and add a new one. This output appears in the console:

[{"selectors":[{"name":"c620","label":"c620","type":1,"active":true,"private":false,"protected":false}],"style":{"padding":"25px","color":"red"}},{"selectors":[{"name":"c1044","label":"c1044","type":1,"active":true,"private":false,"protected":false}],"style":{"padding":"10px"}}]

The deleted element's styles are still present.

Environment:

• Using version 0.15.5 of GrapesJS
• Tested on: Chrome 76.0.3809.132 and Firefox 69 on Ubuntu 18.04.3