identity: Don't let subs be re-registered (#6667)

* Fixes and tests

* Don't set subs be re-registered.

Also allow subs to de-register themselves and collect the deposit.

Also allow individual registering and removal of subs.

* Make it build

* Update frame/identity/src/lib.rs

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

* Tests

* Add benchmarks

* Add some reasonable weights

* Docs

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>

Author: gavofyork

benchmarking/src/mock.rs

@@ -33,7 +33,7 @@ type Staking = pallet_staking::Module<Test>;
 type Session = pallet_session::Module<Test>;
 
 impl_outer_origin! {
-	pub enum Origin for Test  where system = frame_system {}
+	pub enum Origin for Test where system = frame_system {}
 }
 
 impl_outer_dispatch! {

src/mock.rs

@@ -41,7 +41,7 @@ impl From<UintAuthorityId> for MockSessionKeys {
 }
 
 impl_outer_origin! {
-	pub enum Origin for Test  where system = frame_system {}
+	pub enum Origin for Test where system = frame_system {}
 }
 
 thread_local! {