Remove PayPal as an option during the installation process

PayPal has stopped supporting its Ruby SDK [1]. From its README:

> This SDK is deprecated. You can continue to use it, but no new
features or support requests will be accepted. For alternatives, please
visit the current SDK homepage on the PayPal Developer Portal

From the PR [2] that introduced the deprecation message:

> There is no team at PayPal that supports this repo right now (and, in
> fact, the documentation for SDK has been removed from the PayPal docs
> site).
>
> My team is in the process of creating replacement SDKs for integrating
> with PayPal, but until those are available our official recommendation
> is to do one of the following:
>
> A) Use the API directly
> B) Continue using the current SDK, but know that no further updates
> will be made outside of necessary security updates

On top of that, the SDK is locked to paypalhttp_ruby lesser than 2 [3],
but Ruby 3 is only supported since that version [4]. That combines to
make it impossible to use Ruby > 3 + Solidus + PayPal extension.

If PayPal restarts giving support to Ruby, we'll add it again as an
option in the installer for solidus_frontend [5].

[1] - https://github.com/paypal/Checkout-Ruby-SDK
[2] - https://github.com/paypal/Checkout-Ruby-SDK/pull/34#issuecomment-1190523120
[3] - https://github.com/paypal/Checkout-Ruby-SDK/blob/7170ecd5656d9e9f96a4d0ce0ee31b59b3a8268b/paypal-checkout-sdk.gemspec#L22
[4] - paypal/paypalhttp_ruby#12 (comment)
[5] - https://github.com/solidusio/solidus_frontend/blob/master/lib/generators/solidus_frontend/install/install_generator.rb

bin/sandbox

@@ -92,8 +92,7 @@ unbundled bin/rails generate solidus:install \
   --auto-accept \
   --user_class=Spree::User \
   --enforce_available_locales=true \
-  --with_authentication=false \
-  --payment-method=none
+  --with_authentication=false
   $@
 
 unbundled bin/rails generate solidus:auth:install \

core/lib/generators/solidus/install/install_generator.rb

@@ -8,11 +8,6 @@ module Solidus
   class InstallGenerator < Rails::Generators::Base
     CORE_MOUNT_ROUTE = "mount Spree::Core::Engine"
 
-    PAYMENT_METHODS = {
-      'paypal' => 'solidus_paypal_commerce_platform',
-      'none' => nil,
-    }
-
     class_option :migrate, type: :boolean, default: true, banner: 'Run Solidus migrations'
     class_option :seed, type: :boolean, default: true, banner: 'Load seed data (migrations must be run)'
     class_option :sample, type: :boolean, default: true, banner: 'Load sample data (migrations must be run)'
@@ -24,11 +19,6 @@ class InstallGenerator < Rails::Generators::Base
     class_option :lib_name, type: :string, default: 'spree'
     class_option :with_authentication, type: :boolean, default: true
     class_option :enforce_available_locales, type: :boolean, default: nil
-    class_option :payment_method,
-                 type: :string,
-                 enum: PAYMENT_METHODS.keys,
-                 default: PAYMENT_METHODS.keys.first,
-                 desc: "Indicates which payment method to install."
 
     def self.source_paths
       paths = superclass.source_paths
@@ -129,25 +119,6 @@ def install_auth_plugin
       end
     end
 
-    def install_payment_method
-      name = options[:payment_method]
-
-      unless options[:auto_accept]
-        available_names = PAYMENT_METHODS.keys
-
-        name = ask("
-  You can select a payment method to be included in the installation process.
-  Please select a payment method name:", limited_to: available_names, default: available_names.first)
-      end
-
-      gem_name = PAYMENT_METHODS.fetch(name)
-
-      if gem_name
-        @plugins_to_be_installed << gem_name
-        @plugin_generators_to_run << "#{gem_name}:install"
-      end
-    end
-
     def include_seed_data
       append_file "db/seeds.rb", <<-RUBY.strip_heredoc