filemerge: move removal of `.orig` extension on temp file close to context
The place where the `.orig` extension is removed in `_maketempfiles()`
doesn't make it clear that it's the backup path, which is why we have
a comment in the code explaining it. Let's instead move it out of the
function and close to where we get it from `backup.path()`, so that
becomes clear.
Differential Revision: https://phab.mercurial-scm.org/D12190
@echo off
powershell -NoProfile -ExecutionPolicy unrestricted -Command "& '%~dp0\editmergeps.ps1' %*"