[pkg] drop support code for pre-2.5.4 python on debian

We require 2.6.

setup.py

@@ -127,9 +127,6 @@ def install(**kwargs):
     if USE_SETUPTOOLS:
         if '--force-manifest' in sys.argv:
             sys.argv.remove('--force-manifest')
-    # install-layout option was introduced in 2.5.3-1~exp1
-    elif sys.version_info < (2, 5, 4) and '--install-layout=deb' in sys.argv:
-        sys.argv.remove('--install-layout=deb')
     if subpackage_of:
         package = subpackage_of + '.' + modname
         kwargs['package_dir'] = {package : '.'}