fix: Only query "getPeersInCall" when using internal signaling

[SystemKeeper]

Currently we query "getPeersInCall" whenever we join a call and whenever new sessions are processed. Both take not into account, that we need that information soley when using internal signaling:

talk-ios/NextcloudTalk/NCCallController.m

Lines 1623 to 1648 in 9d0b558

	- (TalkActor * _Nullable)getActorFromSessionId:(NSString *)sessionId
	{
	[[WebRTCCommon shared] assertQueue];
	if (_externalSignalingController) {
	return [_externalSignalingController getParticipantFromSessionId:sessionId].actor;
	}
	NSInteger callAPIVersion = [[NCAPIController sharedInstance] callAPIVersionForAccount:_account];
	for (NSMutableDictionary *user in _peersInCall) {
	NSString *userSessionId = [user objectForKey:@"sessionId"];
	if ([userSessionId isEqualToString:sessionId]) {
	TalkActor *actor = [[TalkActor alloc] initWithActorId:[user objectForKey:@"userId"] actorType:@"users" actorDisplayName:[user objectForKey:@"displayName"]];
	if (callAPIVersion >= APIv3) {
	[actor setId:[user objectForKey:@"actorId"]];
	[actor setType:[user objectForKey:@"actorType"]];
	}
	return actor;
	}
	}
	return nil;
	}