Remove Ahoy ensure_uuid logic and uuidtools dependency

Ahoy 2.0.0 [1] introduced automatic UUID generation for visit_token and
visitor_token. As a result, the custom ensure_uuid method is no longer
needed and can be safely removed from the initializer.

Since we aren't manually generating UUIDs anymore, we no longer need
the uuidtools dependency.

[1] https://github.com/ankane/ahoy/blob/v2.0.0/README.md#token-generation

config/initializers/ahoy.rb

@@ -8,17 +8,17 @@ class Ahoy::Store < Ahoy::DatabaseStore
   end
 
   def track_visit(data)
-    data[:id] = ensure_uuid(data.delete(:visit_token))
-    data[:visitor_id] = ensure_uuid(data.delete(:visitor_token))
+    data[:id] = ahoy.visit_token
+    data[:visitor_id] = ahoy.visitor_token
     super(data)
   end
 
   def visit
     unless defined?(@visit)
       if ahoy.send(:existing_visit_token) || ahoy.instance_variable_get(:@visit_token)
-        @visit = visit_model.where(id: ensure_uuid(ahoy.visit_token)).take if ahoy.visit_token
+        @visit = visit_model.where(id: ahoy.visit_token).take if ahoy.visit_token
       elsif !Ahoy.cookies? && ahoy.visitor_token
-        @visit = visit_model.where(visitor_id: ensure_uuid(ahoy.visitor_token))
+        @visit = visit_model.where(visitor_id: ahoy.visitor_token)
                             .where(started_at: Ahoy.visit_duration.ago..)
                             .order(started_at: :desc)
                             .first
@@ -34,12 +34,6 @@ class Ahoy::Store < Ahoy::DatabaseStore
     Visit
   end
 
-  def ensure_uuid(id)
-    UUIDTools::UUID.parse(id).to_s
-  rescue
-    UUIDTools::UUID.sha1_create(UUIDTools::UUID.parse(Ahoy::Tracker::UUID_NAMESPACE), id).to_s
-  end
-
   def exclude?
     false
   end