Update composition-api-setup.md (#1427)

* Update composition-api-setup.md

From the source code, when the setup function is called, the component instance is already created using the createComponentInstance function.

* Update src/guide/composition-api-setup.md

Co-authored-by: Natalia Tepluhina <[email protected]>

Co-authored-by: Natalia Tepluhina <[email protected]>

Author: chenfan0

src/guide/composition-api-setup.md

@@ -103,7 +103,7 @@ We'll explain the role of `expose` shortly.
 
 ## Accessing Component Properties
 
-When `setup` is executed, the component instance has not been created yet. As a result, you will only be able to access the following properties:
+When `setup` is executed, you will only be able to access the following properties:
 
 - `props`
 - `attrs`