Instructions for removal

[xeruf]

https://guides.solidus.io/developers/payments/payment-service-providers#switching-payment-service-provider tells me to use:

❯ bin/rake payment_method:deactivate_unsupported_payment_methods
Running via Spring preloader in process 89966
rake aborted!
Don't know how to build task 'payment_method:deactivate_unsupported_payment_methods' (See the list of available tasks with `rake --tasks`)

And either way, stuff fails: the config file, the route - rake cannot even start with all that in place, so it would be nice to add instructions here or in general in the docs for removal