style(NcAppSidebar): remove custom styles from close button

Signed-off-by: Maksim Sukharev <antreesy.web@gmail.com>

Author: Antreesy

src/components/NcAppSidebar/NcAppSidebar.vue

@@ -1336,14 +1336,6 @@ $top-buttons-spacing: $app-navigation-padding; // align with app navigation
 			inset-inline-end: $top-buttons-spacing;
 			width: var(--default-clickable-area);
 			height: var(--default-clickable-area);
-			opacity: $opacity_normal;
-			border-radius: calc(var(--default-clickable-area) / 2);
-			&:hover,
-			&:active,
-			&:focus {
-				opacity: $opacity_full;
-				background-color: $action-background-hover;
-			}
 		}
 
 		// Compact mode only affects a sidebar with a figure