While it is possible to select a formatted citation (including any delimiters) and press the delete key on your keyboard, this is not the recommended method. If you do not completely delete the citation, you could corrupt your document.
To safely delete a formatted citation:
In Pages, highlight the citation you want to delete.
Display the Manage Citations dialog in one of these ways:
Double-click on the citation.
From the Control+Click context-sensitive menu, select Edit Citation.
From the Edit menu, select EndNote Citations, and then select Manage Citations.
All of the cited references in the document are listed in the dialog. The citation you highlighted in the document should be highlighted in the list. Make sure the highlighted citation is the one you want to delete.
Click the minus sign at the left of the dialog.