Serial: remove intermediate_buffer leftover #1208

Job	Run time
compile-examples (arduino:mbed:nano33ble, nano33ble)	12m 17s
compile-examples (arduino:mbed:envie_m7, envie_m7)	16m 58s
compile-examples (arduino:mbed:envie_m7:target_core=cm4, envie_m7_core_cm4)	4m 30s
compile-examples (arduino:mbed:nanorp2040connect, nanorp2040connect)	21m 36s
compile-examples (arduino:mbed:nicla_sense, nicla_sense)	22m 35s
compile-examples (arduino:mbed:nicla_vision, nicla_vision)	19m 7s
compile-examples (arduino:mbed:opta, opta)	23m 23s
compile-examples (arduino:mbed:giga, giga)	37m 43s
compile-examples (arduino:mbed:nicla_voice, nicla_voice)	8m 30s
compile-examples (arduino:mbed:edge_control, edge_control)	8m 42s
	2h 55m 21s

Provide feedback