Remove deregisterIdentity()

Remove the ability to remove registered identities. Once registered, identities are part
of a permanent record (for example you would want to ensure parties to contracts cannot
"disappear" by removing themselves from the identity service).

core/src/main/kotlin/core/node/services/IdentityService.kt

@@ -10,7 +10,11 @@ import java.security.PublicKey
  */
 interface IdentityService {
     fun registerIdentity(party: Party)
-    fun deregisterIdentity(party: Party)
+
+    // There is no method for removing identities, as once we are made aware of a Party we want to keep track of them
+    // indefinitely. It may be that in the long term we need to drop or archive very old Party information for space,
+    // but for now this is not supported.
+
     fun partyFromKey(key: PublicKey): Party?
     fun partyFromName(name: String): Party?
 }

src/main/kotlin/core/node/services/InMemoryIdentityService.kt

@@ -17,10 +17,7 @@ class InMemoryIdentityService() : IdentityService {
         keyToParties[party.owningKey] = party
         nameToParties[party.name] = party
     }
-    override fun deregisterIdentity(party: Party) {
-        keyToParties.remove(party.owningKey)
-        nameToParties.remove(party.name)
-    }
+
     override fun partyFromKey(key: PublicKey): Party? = keyToParties[key]
     override fun partyFromName(name: String): Party? = nameToParties[name]
 }

src/main/kotlin/core/testing/MockIdentityService.kt

@@ -19,7 +19,6 @@ class MockIdentityService(val identities: List<Party>) : IdentityService {
         get() = synchronized(identities) { identities.associateBy { it.name } }
 
     override fun registerIdentity(party: Party) { throw UnsupportedOperationException() }
-    override fun deregisterIdentity(party: Party) { throw UnsupportedOperationException() }
     override fun partyFromKey(key: PublicKey): Party? = keyToParties[key]
     override fun partyFromName(name: String): Party? = nameToParties[name]
 }