charging-sdl does not work properly

We've had charging-sdl in pmaports for over 3 years, which is also the same time where the last actual code commit was committed. Unfortunately it's not working well or at all for many devices. It's also a very basic application which does nothing to actually help the charging process, like switching everything to low-power modes to charge as quickly as possible. Additionally our main device, the PinePhone is not supported at all by charging-sdl due to the bootloader not adding a cmdline argument that we could use.

In my opinion there is no advantage to keeping charging-sdl in the initfs, due to the aforementioned reasons. Removing it will also solve various downsides where the boot would hang at charging-sdl because the device was booted from a charger which can be quite annoying.