local: use agent token to deregister services

.changelog/9683.txt

@@ -0,0 +1,3 @@
+```release-notes:improvement
+client: when a client agent is attempting to dereigster a service, anddoes not have access to the ACL token used to register a service, attempt to use the agent token instead of the default user token. If no agent token is set, fall back to the default user token.
+```

agent/local/state.go

@@ -243,7 +243,7 @@ func (l *State) serviceToken(id structs.ServiceID) string {
 		token = s.Token
 	}
 	if token == "" {
-		token = l.tokens.UserToken()
+		token = l.tokens.AgentToken()
 	}
 	return token
 }
@@ -457,7 +457,7 @@ func (l *State) checkToken(id structs.CheckID) string {
 		token = c.Token
 	}
 	if token == "" {
-		token = l.tokens.UserToken()
+		token = l.tokens.AgentToken()
 	}
 	return token
 }