filemerge: when merge tool uses $output, don't leave markers in $local
As explained in the previous patch, we incorrectly leave conflict
markers in both `$local` and `$output` since D12190. I don't
understand why it broke but the fix is simple and clear after all the
recent refactoring.
Differential Revision: https://phab.mercurial-scm.org/D12379
[build-system]
requires = ["setuptools", "wheel"]
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true