🎨 (Marshmallow) Undo changes to schemas in Smorest project

Using `PlainItemSchema` and `PlainStoreSchema` as names for schemas that don't have `Nested` fields makes sense, but in this project we don't have `Nested` fields, so it feels difficult to justify. We will adopt this naming convention in the following section, when we do have nesting.

Author: jslvtr

project/03-items-stores-smorest/schemas.py

@@ -1,26 +1,18 @@
 from marshmallow import Schema, fields
 
 
-class PlainItemSchema(Schema):
-    id = fields.Int(dump_only=True)
+class ItemSchema(Schema):
+    id = fields.Str(dump_only=True)
     name = fields.Str(required=True)
     price = fields.Float(required=True)
-
-
-class PlainStoreSchema(Schema):
-    id = fields.Int(dump_only=True)
-    name = fields.Str()
-
-
-class ItemSchema(PlainItemSchema):
-    store_id = fields.Int(required=True, load_only=True)
-    store = fields.Nested(lambda: PlainStoreSchema(), dump_only=True)
+    store_id = fields.Int(required=True)
 
 
 class ItemUpdateSchema(Schema):
     name = fields.Str()
     price = fields.Float()
 
 
-class StoreSchema(PlainStoreSchema):
-    items = fields.List(fields.Nested(PlainItemSchema()), dump_only=True)
+class StoreSchema(Schema):
+    id = fields.Str(dump_only=True)
+    name = fields.Str(required=True)