refactor: clean up Player::OnEnterSystem

The call to ResetHyperspaceTarget in Player::OnEnterSystem has been
superfluous since probably commit
1e2e471.

As there was a comment that the SectorView should not be invoked from
this callback, and recent testing showed that it did not impact the game
logic, lets remove it and resolve the comment.

src/Player.cpp

@@ -209,8 +209,6 @@ void Player::OnEnterHyperspace()
 void Player::OnEnterSystem()
 {
 	m_controller->SetFlightControlState(CONTROL_MANUAL);
-	//XXX don't call sectorview from here, use signals instead
-	Pi::game->GetSectorView()->ResetHyperspaceTarget();
 }
 
 //temporary targeting stuff