slam_tomb: adjust for changes in list_tomb_mounts

As the argument for list_tomb_mounts uses the input directly, it needs to be uniform.
Therefore one must make sure that extraneous character like parentheses are removed from the variable.
And those are in place in tombname for slam_tomb().

tomb

@@ -3162,7 +3162,7 @@ slam_tomb() {
 				result=1 }
 		done
 		# if it failed killing a process, report it
-		[[ $result = 0 ]] && umount_tomb $tombname
+		[[ $result = 0 ]] && umount_tomb "${tombname:1:-1}"
 	done
 	return $result
 }
@@ -3378,7 +3378,7 @@ main() {
 
 		# Slam a tomb killing all processes running inside
 		slam)
-			slam_tomb $PARAM
+			slam_tomb $PARAM[1]
 			;;
 
 		# Close the tomb