So would it simply be possible to delete “main” file of the ranging examples and create ones own application?
Yes, this is certainly possible. Whether you should depends on what you want to do. The PANS system is a pretty advanced demo allowing easy access to positioning of tags while still being extensible by allowing to run a user application next to the TWR and BLE stacks. If you want to develop your own system, including implementing a custom ranging algorithm, you can use the deca_driver library directly.
The output looks correct. If the node is configured as a tag and enough anchors are in range it should also start printing the position, though to be fair I didn’t test this myself yet.
Where would I look to learn these functions, if the definitions even are publicly available.
The functions are described in section 5, API functions description, of the DWM1001 Firmware API Guide, located under DWM1001_DWM1001-DEV_MDEK1001_Sources_and_Docs_v9\DWM1001\Product_and_Design_Documents in the support package.
I also suggest to read the System Overview to get a better understanding of how the PANS system works.
If you want to start a project from scratch (i.e without PANS and/or Nordic Softdevice), I suggest looking at the examples we provide for the DWM1004. These run directly on the MCU and include some TWR algorithms, but you will have to adept them to run on the NRF52 MCU of the DWM1001 the DWM1001 examples on Github. See also the forum thread discussing these examples.