serial: 8250_pci: Remove empty stub pci_quatech_exit()

The ->exit() callback is checked for presence anyway,
no need to have an empty stub.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211026133452.61657-2-andriy.shevchenko@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>