Remove extern crate from code samples

Author: dtolnay

src/interoperability.md

@@ -135,10 +135,7 @@ serde = { version = "1.0", optional = true }
 ```
 
 ```rust
-#[cfg(feature = "serde")]
-extern crate serde;
-
-struct T { /* ... */ }
+pub struct T { /* ... */ }
 
 #[cfg(feature = "serde")]
 impl Serialize for T { /* ... */ }
@@ -155,12 +152,8 @@ serde = { version = "1.0", optional = true, features = ["derive"] }
 ```
 
 ```rust
-#[cfg(feature = "serde")]
-#[macro_use]
-extern crate serde;
-
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
-struct T { /* ... */ }
+pub struct T { /* ... */ }
 ```
 
 

src/type-safety.md

@@ -94,8 +94,7 @@ provides a typesafe representation of this pattern.
 [`bitflags`]: https://github.com/bitflags/bitflags
 
 ```rust
-#[macro_use]
-extern crate bitflags;
+use bitflags::bitflags;
 
 bitflags! {
     struct Flags: u32 {