Remove Unnecessary spree_frontend gem

[edmondchui]

In the pull request for Spree 4.5 update, spree_frontend gem was introduced as a gem dependency. Since I don't use spree_frontend, I got following error when starting my Spree server:

~/.rbenv/versions/3.2.2/lib/ruby/gems/3.2.0/gems/spree_auth_devise-4.5.0/lib/controllers/frontend/spree/auth/checkout_controller_decorator.rb:45:in `<top (required)>': uninitialized constant Spree::CheckoutController (NameError)

Spree::CheckoutController.prepend(Spree::Auth::CheckoutControllerDecorator)
     ^^^^^^^^^^^^^^^^^^^^
	from <internal:/Users/echui/.rbenv/versions/3.2.2/lib/ruby/site_ruby/3.2.0/rubygems/core_ext/kernel_require.rb>:38:in `require'

Also spree_frontend is mentioned in the Update Gemfile section in Spree 4.5 tp 4.6 migration guide, it should not be added for those not using spree_frontend.

I'm requesting to remove spree_frontend from the gemspec.

[iaderblocklack]

@edmondchui do you found how to solve this issue? I have the same error

[edmondchui]

@iaderblocklack I've already created this pull request #198 (reference) a while back.
Just need someone to merge.