Remove required from tracker_project_name (huggingface#3260)

Remove required from tracker_project_name.

As observed by https://github.com/off99555 in huggingface#2695 (comment), it already has a default value.

Author: pcuenca

examples/controlnet/train_controlnet.py

@@ -536,7 +536,6 @@ def parse_args(input_args=None):
         "--tracker_project_name",
         type=str,
         default="train_controlnet",
-        required=True,
         help=(
             "The `project_name` argument passed to Accelerator.init_trackers for"
             " more information see https://huggingface.co/docs/accelerate/v0.17.0/en/package_reference/accelerator#accelerate.Accelerator"