ArgumentDefaultsHelpFormatter: fix docstring

[ferdnyc]

In #27808 @michiboo @abadger enhanced the display of default values in argparse help messages. Unfortunately, the docstring for argparse.ArgumentDefaultsHelpFormatter got somewhat garbled along the way.

• Originally, commit 336bd2f added a new function, _add_defaults_to_help_string, documented as:

  Add the default value to the option help message.

  ArgumentDefaultsHelpFormatter and BooleanOptionalAction both want to add the default value to the help message when it isn't already present. This code will do that, detecting cornercases to prevent duplicates or cases where it wouldn't make sense to the end user.

• But subsequent commit dc4babf incorporated that functionality into argparse.ArgumentDefaultsHelpFormatter._get_help_string instead, and its docstring was set to:

  Add the default value to the option help message.

  ArgumentDefaultsHelpFormatter and BooleanOptionalAction when it isn't already present. This code will do that, detecting cornercases to prevent duplicates or cases where it wouldn't make sense to the end user.

This PR clears up and simplifies removes that docstring, as it didn't really add information not discernible just by reading the code.

[ferdnyc]

@michiboo Do you have a moment to look at this? It's purely a docstring adjustment, related to your previous changes to argparse's ArgumentDefaultsHelpFormatter.

[ferdnyc]

My apologies, the PR in question was @abadger's, based on an earlier PR by @michiboo.

@abadger, do you have a moment to look at this? It's purely a docstring adjustment, related to your previous changes to argparse's ArgumentDefaultsHelpFormatter.

[serhiy-storchaka]

Thank you for reporting and fixing this issue.