Remove memoizer from api

If you aren't using default setup, you'll need to add this back in.

```
use Flipper::Api.app(flipper, env_key: "flipper_api") do |builder|
  builder.use Flipper::Api::Memoizer, flipper, env_key: "flipper_api"
end
```

Author: jnunemaker

lib/flipper/api.rb

@@ -15,9 +15,7 @@ def self.app(flipper = nil, options = {})
       builder = Rack::Builder.new
       yield builder if block_given?
       builder.use Flipper::Api::JsonParams
-      builder.use Flipper::Middleware::SetupEnv, flipper, env_key: env_key
-      builder.use Flipper::Middleware::Memoizer, memoizer_options.merge(env_key: env_key)
-      builder.use Flipper::Api::Middleware, env_key: env_key
+      builder.use Flipper::Api::Middleware, flipper, env_key: env_key
       builder.run app
       klass = self
       builder.define_singleton_method(:inspect) { klass.inspect } # pretty rake routes output

lib/flipper/api/middleware.rb

@@ -9,10 +9,16 @@
 module Flipper
   module Api
     class Middleware
-      def initialize(app, options = {})
+      def initialize(app, flipper = nil, options = {})
         @app = app
         @env_key = options.fetch(:env_key, 'flipper')
 
+        if flipper.respond_to?(:call)
+          @flipper_block = flipper
+        else
+          @flipper = flipper || Flipper
+        end
+
         @action_collection = ActionCollection.new
         @action_collection.add Api::V1::Actions::PercentageOfTimeGate
         @action_collection.add Api::V1::Actions::PercentageOfActorsGate
@@ -32,13 +38,19 @@ def call(env)
       def call!(env)
         request = Rack::Request.new(env)
         action_class = @action_collection.action_for_request(request)
+
         if action_class.nil?
           @app.call(env)
         else
-          flipper = env.fetch(@env_key)
-          action_class.run(flipper, request)
+          action_class.run(env[@env_key] || flipper, request)
         end
       end
+
+      private
+
+      def flipper
+        @flipper ||= @flipper_block.call
+      end
     end
   end
 end