formatter: inline a variable assigned from `templater.templater.frommapfile`

The variable doesn't get reused and it doesn't help formatting, so I
don't see any reason for it.

Differential Revision: https://phab.mercurial-scm.org/D8807

mercurial/formatter.py

@@ -626,8 +626,7 b' def loadtemplater(ui, spec, defaults=Non'
     a map file"""
     assert not (spec.tmpl and spec.mapfile)
     if spec.mapfile:
-        frommapfile = templater.templater.frommapfile
-        return frommapfile(
+        return templater.templater.frommapfile(
             spec.mapfile, defaults=defaults, resources=resources, cache=cache
         )
     return maketemplater(