hghave: remove py27+ capability

It is now unused. And we require Python 2.7+ now so this check is not
necessary.

tests/hghave.py

@@ -580,10 +580,6 b' def has_absimport():'
     from mercurial import util
     return util.safehasattr(__future__, "absolute_import")
 
-@check("py27+", "running with Python 2.7+")
-def has_python27ornewer():
-    return sys.version_info[0:2] >= (2, 7)
-
 @check("py3k", "running with Python 3.x")
 def has_py3k():
     return 3 == sys.version_info[0]