remotefilelog: fix {file_copies} template keyword

Authored by martinvonz.

Description

remotefilelog: fix {file_copies} template keyword

remotefilelog overrides templatekw.getrenamedfn(). I changed the
return type of that function in ec37df9042f9 (templatekw: make
getrenamed() return only filename, not nodeid, 2018-03-26). So we need
to change remotefilelog too. The function is used by the {file_copies}
template keyword and by hg log --copies.

Differential Revision: https://phab.mercurial-scm.org/D5576

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