optimize: remove fsync when dumping rwlock data (#4052)

Fixes #3653

dvc/rwlock.py

@@ -51,9 +51,6 @@ def _edit_rwlock(lock_dir):
     yield lock
     with open(path, "w+") as fobj:
         json.dump(lock, fobj)
-        # NOTE: flush and fsync to ensure that rwlock contents are saved
-        fobj.flush()
-        os.fsync(fobj.fileno())
 
 
 def _infos_to_str(infos):

tests/func/test_repro_multistage.py

@@ -449,7 +449,7 @@ def test_repro_when_new_outs_added_does_not_exist(tmp_dir, dvc):
         {
             "stages": {
                 "run-copy": {
-                    "cmd": "python copy {} {}".format("foo", "foobar"),
+                    "cmd": "python copy.py {} {}".format("foo", "foobar"),
                     "deps": ["foo"],
                     "outs": ["foobar", "bar"],
                 }