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

tests/extmod/uctypes_le.py

tests/extmod/uctypes_le_float.py

tests/extmod/uctypes_native_float.py

tests/extmod/uctypes_native_le.py

tests/extmod/uctypes_print.py

tests/extmod/uctypes_ptr_le.py

tests/extmod/uctypes_ptr_native_le.py

tests/extmod/uctypes_sizeof.py

tests/extmod/uctypes_sizeof_native.py

tests/extmod/uhashlib_sha1.py

tests/extmod/uhashlib_sha256.py

tests/extmod/uheapq1.py

tests/extmod/ujson_dumps.py

tests/extmod/ujson_dumps_extra.py

tests/extmod/ujson_dumps_float.py

tests/extmod/ujson_load.py

tests/extmod/ujson_loads.py

tests/extmod/ujson_loads_float.py

tests/extmod/urandom_basic.py

tests/extmod/urandom_extra.py