filemerge: remove `uselocalpath` argument from `_maketempfiles()` The `localpath` argument is unused if `uselocalpath` is false, so we can use `None` as a sentinel value for the variable instead and remove extra `uselocalpath` argument. That's not much of a win, but it's a small step towards further improvements. Differential Revision: https://phab.mercurial-scm.org/D12189

# Files that just need to be migrated to the formatter.
# Do not add new files here!
mercurial/cext/manifest.c
mercurial/cext/osutil.c
# Vendored code that we should never format:
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contrib/python-zstandard/**.c
contrib/python-zstandard/**.h
hgext/fsmonitor/pywatchman/**.c
mercurial/thirdparty/**.c
mercurial/thirdparty/**.h
mercurial/pythoncapi_compat.h