Simplify node, profile, and image completions

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

internal/app/wwctl/image/show/root.go

@@ -12,9 +12,14 @@ var (
 		Short:                 "Show root fs dir for image",
 		Long: `Shows the base directory for the chroot of the given image.
 More information about the image can be shown with the '-a' option.`,
-		RunE:              CobraRunE,
-		ValidArgsFunction: completions.Images(0), // no limit
-		Args:              cobra.ExactArgs(1),
+		RunE: CobraRunE,
+		Args: cobra.ExactArgs(1),
+		ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			if len(args) == 0 {
+				return completions.Images(cmd, args, toComplete)
+			}
+			return completions.None(cmd, args, toComplete)
+		},
 	}
 	ShowAll bool
 )