The Curves viewThe area in the Timeline Editor window that shows the animation curves for Infinite clips or for Animation clips that have been converted from Infinite clips. The Curves view is similar to Curves mode in the Animation window. More info
See in Glossary provides the following methods for deleting keys:
Right-click a key and select Delete Key from the context menu. This method does not affect selected keys.
Select a key and either press Delete or right-click and select Delete Key from the context menu.