fix(coachmark): remove unused custom property

Author: cdransf

components/coachmark/index.css

@@ -25,7 +25,6 @@
 	/* layout */
 	--spectrum-coachmark-padding: var(--spectrum-coach-mark-edge-to-content);
 	--spectrum-coachmark-image-to-heading: var(--spectrum-coach-mark-edge-to-content);
-	--spectrum-coachmark-heading-to-action-button: var(--spectrum-spacing-300);
 	--spectrum-coachmark-header-to-body: var(--spectrum-spacing-200);
 	--spectrum-coachmark-body-to-footer: var(--spectrum-spacing-300);