templatekw: make getrenamed() return only filename, not nodeid
No callers cared about the nodeid and I want to make getrenamed() not
look up the node (although it's currently free, I hope to store copy
info in changesets and not include the nodeid).
Differential Revision: https://phab.mercurial-scm.org/D3666
#require docutils gettext
$ $TESTDIR/check-gendoc it
checking for parse errors