extdiff: remove dir2root and pass full path as dir2 in _runperfilediff()
The only use of `dir2root` was to join with `dir2` to generate the path for
other side of diff. Like in previous patch, `dir1a` and `dir1b` are full paths
and no longer base names, hence we pass `dir2` as full path too and making
`dir2root` unrequired.
Differential Revision: https://phab.mercurial-scm.org/D8970
# black pulls in typed-ast, which doesn't install on PyPy.
black ; python_version >= '3.6' and platform_python_implementation != 'PyPy'
# Bazaar doesn't work with Python 3 nor PyPy.
bzr ; python_version <= '2.7' and platform_python_implementation == 'CPython'
docutils
fuzzywuzzy
pyflakes
pygments
pylint
# Needed to avoid warnings from fuzzywuzzy.
python-Levenshtein
# typed-ast dependency doesn't install on PyPy.
typed-ast ; python_version >= '3.0' and platform_python_implementation != 'PyPy'
vcrpy