Don't remove files that don't exist

[CJ-Wright]

I think this is causing an issue with the ci-skeleton feature where it is trying to delete __pycache__ but the folder doesn't exist.

Checklist

• Added a news entry

[isuruf]

Can you show a traceback?

[CJ-Wright]

Traceback (most recent call last):
  File "/home/christopher/mc/bin/conda-smithy", line 33, in <module>
    sys.exit(load_entry_point('conda-smithy', 'console_scripts', 'conda-smithy')())
  File "/home/christopher/dev/conda-smithy/conda_smithy/cli.py", line 613, in main
    args.subcommand_func(args)
  File "/home/christopher/dev/conda-smithy/conda_smithy/cli.py", line 419, in __call__
    self._call(args, tmpdir)
  File "/home/christopher/dev/conda-smithy/conda_smithy/cli.py", line 430, in _call
    temporary_directory=temporary_directory,
  File "/home/christopher/dev/conda-smithy/conda_smithy/configure_feedstock.py", line 1909, in main
    config = _load_forge_config(forge_dir, exclusive_config_file)
  File "/home/christopher/dev/conda-smithy/conda_smithy/configure_feedstock.py", line 1614, in _load_forge_config
    remove_file_or_dir(file_with_path)
  File "/home/christopher/dev/conda-smithy/conda_smithy/feedstock_io.py", line 67, in remove_file_or_dir
    repo.index.remove([filename], r=True)
  File "/home/christopher/mc/lib/python3.7/site-packages/git/index/util.py", line 58, in post_clear_cache_if_not_raised
    rval = func(self, *args, **kwargs)
  File "/home/christopher/mc/lib/python3.7/site-packages/git/index/util.py", line 76, in check_default_index
    return func(self, *args, **kwargs)
  File "/home/christopher/mc/lib/python3.7/site-packages/git/index/base.py", line 862, in remove
    removed_paths = self.repo.git.rm(args, paths, **kwargs).splitlines()
  File "/home/christopher/mc/lib/python3.7/site-packages/git/cmd.py", line 542, in <lambda>
    return lambda *args, **kwargs: self._call_process(name, *args, **kwargs)
  File "/home/christopher/mc/lib/python3.7/site-packages/git/cmd.py", line 1005, in _call_process
    return self.execute(call, **exec_kwargs)
  File "/home/christopher/mc/lib/python3.7/site-packages/git/cmd.py", line 822, in execute
    raise GitCommandError(command, status, stderr_value, stdout_value)
git.exc.GitCommandError: Cmd('git') failed due to: exit code(128)
  cmdline: git rm -r --cached -- __pycache__
  stderr: 'fatal: pathspec '__pycache__' did not match any files'

[CJ-Wright]

The issue is that __pycache__ exists but it isn't git tracked so when we try remove it from git, git balks.