remove deprecated configuration from README

[cou929]

I've set up a project with carrierwave and fog-google following the README. And got a deprecation warning message.

DEPRECATION WARNING: #fog_provider is deprecated and has no effect (called from block in <main> at /Users/cou929/Desktop/ws-fog/test_carrierwave/config/initializers/carrierwave.rb:4)

# config/initializers/carrierwave.rb

CarrierWave.configure do |config|
    config.fog_provider = 'fog/google'
    config.fog_credentials = {
        provider:               'Google',
        google_project:         'my-project',
        google_json_key_string: 'xxxxxx'
        # or use google_json_key_location if using an actual file
    }
    config.fog_directory = 'google_cloud_storage_bucket_name'
end

It seems that the config.fog_provider was already deprecated but came back to README after that.

[mshibuya]

Good catch, thank you!