There are two ways to delete selections:
From the symbol selection listing area.
From directly within the editor.
Deleting a selection from the symbol selection listing area
This is the most common method for deleting selections and is covered here.
Deleting a selection from directly within the editor
An alternative method for deleting selections is to use deselect all from within the editor:
Open the editor (Shortcut = E)
Deselect all elements (Shortcut = D)
Close / save the editor (Shortcut = E)
Using the above workflow will result in the selection you used "Deselect all" on being deleted.
Combine with selection review (Shortcut = up / down arrow keys)
When used in combination with the up / down arrow keys to cycle through selections within the editor, it forms an extremely fast workflow for reviewing and deleting selections.
In the above clip, you can see the editor is opened, the up / down arrow keys are used to quickly review each selection, and then deselect all (Shortcut = D) and save edit (Shortcut = E) is used to delete the two selections requiring deletion.
How to: Understand the symbol selection list.