doc: develop: tools: drop platformio docs

PlatformIO seems to not keep up with Zephyr (they don't seem to even
support 3.0), so we should not recommend it as an IDE as part of our
official docs. Also, it is frequent to see people reporting problems on
our Discord channels.

Ref. https://github.com/platformio/platform-ststm32/issues/602

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

doc/develop/tools/index.rst

@@ -7,4 +7,3 @@ Tools and IDEs
    :maxdepth: 1
 
    coccinelle.rst
-   platformio/index.rst

doc/develop/tools/platformio/index.rst

@@ -1,64 +0,0 @@
-.. _platformio:
-
-Using with PlatformIO
-#####################
-
-.. image:: img/platformio-logo.png
-  :target: https://platformio.org/?utm_source=docs.zephyrproject.org
-
-.. contents::
-    :local:
-
-What is PlatformIO?
-*******************
-
-`PlatformIO <https://platformio.org/?utm_source=docs.zephyrproject.org>`__
-is a cross-platform embedded development environment with
-Zephyr support maintained by its developers.
-
-Since Zephyr support within PlatformIO is not maintained by the Zephyr Project,
-please report any issues with PlatformIO directly to its developers in
-`the official PlatformIO repositories <https://github.com/platformio>`_.
-
-A detailed overview of the PlatformIO ecosystem and its philosophy can be
-found in `the official PlatformIO documentation <https://docs.platformio.org/en/latest/what-is-platformio.html?utm_source=docs.zephyrproject.org>`_.
-
-Installation
-************
-
-* `PlatformIO IDE <https://platformio.org/platformio-ide?utm_source=docs.zephyrproject.org>`_
-  is a toolset for embedded C/C++ development available on Windows, macOS and Linux
-  platforms
-* `PlatformIO Core (CLI) <https://docs.platformio.org/en/latest/core/index.html?utm_source=docs.zephyrproject.org>`_
-  is a command-line tool that consists of multi-platform build system, platform and
-  library managers and other integration components. It can be used with a variety of
-  code development environments and allows integration with cloud platforms and web
-  services
-
-Configuration
-*************
-
-Please go through `the official PlatformIO configuration guide for Zephyr project <https://docs.platformio.org/en/latest/frameworks/zephyr.html?utm_source=docs.zephyrproject.org#configuration>`_.
-
-Tutorials
-*********
-
-- `Zephyr and Nordic nRF52-DK: debugging, unit testing, project analysis
-  <https://docs.platformio.org/en/latest/tutorials/nordicnrf52/zephyr_debugging_unit_testing_inspect.html?utm_source=docs.zephyrproject.org>`_
-- `Developing Zephyr RTOS embedded applications on PlatformIO and simulating on Antmicro Renode
-  <https://www.zephyrproject.org/developing-zephyr-rtos-embedded-applications-on-platformio-and-simulating-on-antmicro-renode/>`_
-
-Project Examples
-****************
-
-Please check `the official examples for various development platforms <https://docs.platformio.org/en/latest/frameworks/zephyr.html?utm_source=docs.zephyrproject.org#examples>`_
-
-Next Steps
-**********
-
-Here are some useful links for exploring the PlatformIO ecosystem:
-
-- Try `other platforms <https://docs.platformio.org/en/latest/frameworks/zephyr.html?utm_source=docs.zephyrproject.org#platforms>`_
-  that support Zephyr project
-- Learn more about `integrations with other IDEs/Text Editors <https://docs.platformio.org/en/latest/integration/ide/index.html?utm_source=docs.zephyrproject.org>`_
-- Get help from `PlatformIO community <https://community.platformio.org/?utm_source=docs.zephyrproject.org>`_