boards/xtensa/esp32/esp32.dts: remove redundant button definition

https://github.com/zephyrproject-rtos/zephyr/commit/7dbb1ff2760ce76279ab1af085f15d231dcaaaa2


added a redundant section for the BOOT button which was already defined.

Signed-off-by: Diego Herranz <diegoherranz@diegoherranz.com>