stm: sdioio: remove unused code related to "SD Card detect pin"
stm: sdioio: remove unused code related to "SD Card detect pin"

.. this probably came from the examples that I studied at the beginning
of implementation.

The card detection feature is unused.  As a "detect pin" is not
sent from the shared-bindings, there is no way to get the correct pin
anyway.  Instead, if code needs to detect the insertion state it can
directly use the pin as GPIO in Python code.

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