Remove method alluxio.shell.command.AbstractShellCommand#getNumOfArgs. This method used to be required for all shell CLI classes implementing AbstractShellCommand to return a constant number of arguments this command expects, so that we could check in AbstractShellCommand#validateArgs if the input to this command is valid.
However, our shell commands are getting more flexible, as it may take different number of arguments. For example, help command could take zero argument or one argument. It becomes less meaningful to have a method requiring constant number of argument.
In the future, we should simply require all implementing class of AbstractShellCommand. We should remove AbstractShellCommand#getNumOfArgs, and update their references.