Update schema.mdx

Simplify description of Query and Mutation types.

I think it's safe not to introduce the `schema` keyword in the second page that beginners will come to when learning about GraphQL. Changing the names of the root operation types is, I assume, rare, and so I'm suggesting with these edits to omit going into that detail.

Author: jonathanberger

src/pages/learn/schema.mdx

@@ -67,16 +67,7 @@ Arguments can be either required or optional. When an argument is optional, we c
 
 ## The Query and Mutation types
 
-Most types in your schema will just be normal object types, but there are two types that are special within a schema:
-
-```graphql
-schema {
-  query: Query
-  mutation: Mutation
-}
-```
-
-Every GraphQL service has a `Query` type and may or may not have a `Mutation` type. These types are the same as a regular object type, but they are special because they define the _entry point_ of every GraphQL query. So if you see a query that looks like:
+There are two special "entry point" types that by default are named `Query` and `Mutation`. These types are the same as a regular object type, but they are special because they define the _entry point_ of every GraphQL query. So if you see a query that looks like:
 
 ```graphql
 # { "graphiql": true }
@@ -101,7 +92,7 @@ type Query {
 
 Mutations work in a similar way - you define fields on the `Mutation` type, and those are available as the root mutation fields you can call in your query.
 
-It's important to remember that other than the special status of being the "entry point" into the schema, the `Query` and `Mutation` types are the same as any other GraphQL object type, and their fields work exactly the same way.
+It's important to remember that other than the special status of being the entry points, the `Query` and `Mutation` types are the same as any other GraphQL object type, and their fields work exactly the same way.
 
 ## Scalar types