boards/stm32f030f4-demo: deprecate board

[crasbe]

Contribution description

The STM32F030F4 Demo board was added in 2019 by @benpicco as a cheap board to run RIOT.
It can indeed be bought reasonably cheap for <2€, but it's also kind of obscure and the RIOT documentation is among the first results for it, which is not necessarily a sign that the board is widely used 😅

Also the board has so little RAM, that it is excluded from many tests and examples anyways:

cbuec@W11nMate:~/RIOTstuff/riot-vanillaice/RIOT$ grep -RnwI -i stm32f030f4-demo . | grep Makefile.ci | wc -l
293

These days it's not worth hassling with the Chinese STM32 boards which more often than not have fake STM32 chips on them, since the Nucleo boards have become so widely available and cheap and don't have fake chips, weird bootloaders and other stuff that makes the development experience annoying.

Testing procedure

Execute BOARD=stm32f030f4-demo make -C tests/sys/shell and observe the wonderful yellow deprecation warning.

Issues/PRs references

Support was added in #12433
Noticed in #22257

Declaration of AI-Tools / LLMs usage:

AI-Tools / LLMs that were used are:

• none

[riot-ci]

Murdock results

✔️ PASSED

393d188 boards/stm32f030f4-demo: deprecate board

Success	Failures	Total	Runtime
470	0	470	05m:05s

Artifacts

• Documentation preview

[benpicco]

I mean you can still buy it ¯\(ツ)/¯

But yea it was mostly a curiosity to support such a cheap board.

[crasbe]

I mean you can still buy it ¯_(ツ)_/¯

Some might say I have a personal vendetta after having spent hours trying to get a fake STM32 working in like 2018.
I built a small PCB with a display and stuff on it to play with on the Chaos Communication Congress with some friends, but after not getting it to work because of the fake chip I was so demotivated that I didn't go to the Congress the next day even though I had a ticket :(

[AnnsAnns]

The Pico 2 spoiled me holy heck those specs are wild. Generally I'd advocate for a warning like "Hey, like, maybe use a board that has more than 16KiB of flash" and then maybe deprecate it in a year? I feel like generally there is not too much harm to having that board in RIOT since afaik we don't have to have special handling for that board (other than disabling it for every test imaginable because tf are you supposed to do with a board that small)