tests: Convert remaining "sys.exit()" to "raise SystemExit".

tests/extmod/websocket_basic.py

tests/io/buffered_writer.py

tests/io/open_append.py

tests/io/open_plus.py

tests/io/resource_stream.py

tests/io/write_ext.py

tests/jni/list.py

tests/jni/object.py

tests/jni/system_out.py

tests/micropython/heapalloc_bytesio.py

tests/micropython/heapalloc_iter.py

tests/micropython/heapalloc_traceback.py

tests/micropython/heapalloc_traceback.py.exp

tests/micropython/kbd_intr.py

tests/micropython/schedule.py

tests/misc/non_compliant.py

tests/misc/print_exception.py

tests/misc/recursive_data.py

tests/misc/recursive_iternext.py

tests/misc/sys_exc_info.py