make pool roles optional (#11411)

* make pool roles optional

* undo lock file changes?

* add migration

* Fix

* fix review comments

substrate/frame/staking/src/lib.rs

@@ -533,10 +533,12 @@ impl<T: Config> StakingLedger<T> {
 	/// case that either the active bonded or some unlocking chunks become dust after slashing.
 	/// Returns the amount of funds actually slashed.
 	///
+	/// `slash_era` is the era in which the slash (which is being enacted now) actually happened.
+	///
 	/// # Note
 	///
-	/// This calls `Config::OnStakerSlash::on_slash` with information as to how the slash
-	/// was applied.
+	/// This calls `Config::OnStakerSlash::on_slash` with information as to how the slash was
+	/// applied.
 	fn slash(
 		&mut self,
 		slash_amount: BalanceOf<T>,
@@ -615,6 +617,7 @@ impl<T: Config> StakingLedger<T> {
 				break
 			}
 		}
+
 		self.unlocking.retain(|c| !c.value.is_zero());
 		T::OnStakerSlash::on_slash(&self.stash, self.active, &slashed_unlocking);
 		pre_slash_total.saturating_sub(self.total)