Remove "Token" from the argument schema

Problem/Motivation

The work in 📌 GitLab CI - PHPCS - Long lines and whitespace errors Fixed highlighted the fact that the argument does not accept a token, though it appears to have originally been designed to. The rest of the code in Smart Date's argument class makes no mention of a token. Instead, there is an argument default class implemented.

Proposed resolution

Remove the lines which reference the token from the argument schema file. An update hook may also be needed to ensure that stored argument schemas reflect the new structure.