Remove the unsupported Python 2.6 from configure

A precursor to nodejs#25878

Author: cclauss

configure

@@ -13,10 +13,10 @@ del _
 
 import sys
 from distutils.spawn import find_executable as which
-if sys.version_info[0] != 2 or sys.version_info[1] not in (6, 7):
-  sys.stderr.write('Please use either Python 2.6 or 2.7')
+if sys.version_info[:2] != (2, 7):
+  sys.stderr.write('Please use either Python 2.7')
 
-  python2 = which('python2') or which('python2.6') or which('python2.7')
+  python2 = which('python2') or which('python2.7')
 
   if python2:
     sys.stderr.write(':\n\n')