demandimport: remove support for Python < 2.5

The removed code was to support an __import__ function that doesn't
support the "level" argument. This argument was added in Python 2.5,
which we no longer support.

mercurial/demandimport.py

@@ -37,17 +37,10 except ImportError:
 
 nothing = object()
 
-try:
     # Python 3 doesn't have relative imports nor level -1.
     level = -1
     if sys.version_info[0] >= 3:
         level = 0
-    _origimport(builtins.__name__, {}, {}, None, level)
-except TypeError: # no level argument
-    def _import(name, globals, locals, fromlist, level):
-        "call _origimport with no level argument"
-        return _origimport(name, globals, locals, fromlist)
-else:
     _import = _origimport
 
 def _hgextimport(importfunc, name, globals, *args):