templatekw: migrate to new method for getting copy info

Differential Revision: https://phab.mercurial-scm.org/D6012

mercurial/templatekw.py

@@ -129,8 +129,7 b' def getrenamedfn(repo, endrev=None):'
         # If linkrev != rev (i.e. rev not found in rcache) fallback to
         # filectx logic.
         try:
-            renamed = repo[rev][fn].renamed()
-            return renamed and renamed[0]
+            return repo[rev][fn].copysource()
         except error.LookupError:
             return None