boards: stm32: Remove Kconfig I2C symbols

Following conversion of stm32 i2c driver to use of DT_NODELABEL
macros, configuration of i2c instance in stm32 boards should
no more be done thanks to Kconfig symbols, but is done thanks
to device tree file.
Clean boards files from these symbols.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
96 files changed