The `get_serial_number()` method in the ChassisBase and ModuleBase classes was redundant, as the `get_serial()` method is inherited from the DeviceBase class. This method was removed from the base classes in sonic-platform-common and the submodule was updated in https://github.com/Azure/sonic-buildimage/pull/5625.
This PR aligns the existing vendor platform API implementations to remove the `get_serial_number()` methods and ensure the `get_serial()` methods are implemented, if they weren't previously.
Note that this PR does not modify the Dell platform API implementations, as this will be handled as part of https://github.com/Azure/sonic-buildimage/pull/5609
