Use LOG_TARGET in consensus related crates (#12875)

* Use shared LOG_TARGET in consensus related crates
* Rename target from "afg" to "grandpa"

substrate/frame/aura/src/lib.rs

@@ -58,6 +58,8 @@ mod tests;
 
 pub use pallet::*;
 
+const LOG_TARGET: &str = "runtime::aura";
+
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
@@ -222,7 +224,7 @@ impl<T: Config> OneSessionHandler<T::AccountId> for Pallet<T> {
 			if last_authorities != next_authorities {
 				if next_authorities.len() as u32 > T::MaxAuthorities::get() {
 					log::warn!(
-						target: "runtime::aura",
+						target: LOG_TARGET,
 						"next authorities list larger than {}, truncating",
 						T::MaxAuthorities::get(),
 					);