modules: Remove unused code and variables

[softwarecki]

Removed unnecessary functions from Processing Module Adapter. To ensure proper operation of native loadable modules it is necessary to bypass Processing Module Adapter used by FDK modules. This is currently done by overriding the pointer to module_interface used by the Module Adapter. Thanks to this, the Module Adapter directly calls functions provided by native module. As in this case the Processing Module Adapter functions are omitted, support for native libraries are removed from it as it is no longer needed. This leads to remove is_native_sof variable and modules_process_raw, modules_process_audio_stream functions.

The code allocating/freeing in_buff and out_buff buffers, which were not used, was removed from the processing module adapter.

The value stored by the Processing Module Adapter in the module_adapter field of module_data structure has been moved to an unused private field. This change allowed the module_adapter field to be removed.

The unused sys_service field has been removed from the processing_module structure. It was never initialized anywhere, and its value was passed as a parameter to the native_system_agent_start function which did not use it.

The value assigned to the module_entry_point field in the module_data structure wasn't used anywhere. This field has been removed.

[dbaluta]

@softwarecki what is native loadable modules? Is the support from Zephyr for loading modules or the one from SOF?

[softwarecki]

@dbaluta:

@softwarecki what is native loadable modules?

We currently have three types of loadable modules...

1. IADK supported by Processing Module Aadapter,
2. native supported by lib_manager
3. llext supported by llext_manager and zephyr.