Update freemodbus component file esp-idf/components/freemodbus/port/portserial.c to remove UART mode settings;
Move UART mode settings into esp-idf/examples/protocols/modbus_slave/main/freemodbus.c
Move UART pin settings from Component config into example Kconfig.projbuild file
Move setup of UART port pins from freemodbus component into example file
TW#27721
Closes https://github.com/espressif/esp-idf/issues/2784#issuecomment-443600157
