Remove unneeded oauth2Login config when upgrading to Spring Security 6

oauth2Login() is a Spring Security feature that allows users to authenticate with an OAuth2 or OpenID Connect 1.0 provider. When a user is authenticated using this feature, they are granted a set of authorities that determines what actions they are allowed to perform within the application. In Spring Security 5, the default authority given to a user authenticated with an OAuth2 or OpenID Connect 1.0 provider via oauth2Login() is ROLE_USER. This means that the user is allowed to access the application's resources as a regular user. However, in Spring Security 6, the default authority given to a user authenticated with an OAuth2 provider is OAUTH2_USER, and the default authority given to a user authenticated with an OpenID Connect 1.0 provider is OIDC_USER. These authorities are more specific and allow for better customization of the user's permissions within the application. If you are upgrading to Spring Security 6 and you have previously configured a GrantedAuthoritiesMapper to handle the authorities of users authenticated via oauth2Login(), you can remove it completely as the new default authorities should be sufficient.