Clarify language in components-and-props.md (#3020)

* Clarify language in components-and-props.md

This is a nit for a few reasons:
- The point that extracting a component that "is complex enough on its own" means that it's not necessarily reusable.
- Extracting the components listed in the same sentence (e.g. App) are not necessarily reusable.
- This ends the section "Extracting Components" with a reference to extraction instead of re-usability.
- This delimits extracting into a separate component from creating a re-usable component.

* Update components-and-props.md

* Update components-and-props.md

content/docs/components-and-props.md

@@ -233,7 +233,7 @@ function Comment(props) {
 
 [](codepen://components-and-props/extracting-components-continued)
 
-Extracting components might seem like grunt work at first, but having a palette of reusable components pays off in larger apps. A good rule of thumb is that if a part of your UI is used several times (`Button`, `Panel`, `Avatar`), or is complex enough on its own (`App`, `FeedStory`, `Comment`), it is a good candidate to be a reusable component.
+Extracting components might seem like grunt work at first, but having a palette of reusable components pays off in larger apps. A good rule of thumb is that if a part of your UI is used several times (`Button`, `Panel`, `Avatar`), or is complex enough on its own (`App`, `FeedStory`, `Comment`), it is a good candidate to be extracted to a separate component.
 
 ## Props are Read-Only {#props-are-read-only}