command: remove default property from "targets" argparse code in

data sync and `commit` commands,
since `None` is the default value for the removed `default` property,
see https://docs.python.org/dev/library/argparse.html#default

dvc/command/commit.py

@@ -67,7 +67,6 @@ def add_parser(subparsers, parent_parser):
     commit_parser.add_argument(
         "targets",
         nargs="*",
-        default=None,
         help="DVC-files to commit. Optional."
         "(Finds all DVC-files in the workspace by default.)",
     )

dvc/command/data_sync.py

@@ -116,7 +116,6 @@ def shared_parent_parser():
     shared_parent_parser.add_argument(
         "targets",
         nargs="*",
-        default=None,
         help="Limit command scope to these DVC-files. "
         "Using -R, directories to search DVC-files in can also be given.",
     )