Remove unnecessary 'extern's.

Change-Id: Iba2b3fb6ff88e504f1657b915120ae43d58a1e03
diff --git a/libc/include/sys/reboot.h b/libc/include/sys/reboot.h
index 7d202f7..df4739e 100644
--- a/libc/include/sys/reboot.h
+++ b/libc/include/sys/reboot.h
@@ -25,6 +25,7 @@
  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
+
 #ifndef _SYS_REBOOT_H_
 #define _SYS_REBOOT_H_
 
@@ -41,7 +42,7 @@
 #define RB_DISABLE_CAD  LINUX_REBOOT_CMD_CAD_OFF
 #define RB_POWER_OFF    LINUX_REBOOT_CMD_POWER_OFF
 
-extern int reboot(int  reboot_type);
+int reboot(int reboot_type);
 
 __END_DECLS