test-module-imports: drop check for Python >= 2.6

Support for Python 2.4 and 2.5 has been dropped. This check is no
longer necessary.

tests/test-module-imports.t

@@ -1,41 +1,37 b''
 #require test-repo
 
-This code uses the ast module, which was new in 2.6, so we'll skip
-this test on anything earlier.
-  $ $PYTHON -c 'import sys ; assert sys.version_info >= (2, 6)' || exit 80
-
   $ import_checker="$TESTDIR"/../contrib/import-checker.py
 
 Run the doctests from the import checker, and make sure
 it's working correctly.
   $ TERM=dumb
   $ export TERM
   $ python -m doctest $import_checker
 
   $ cd "$TESTDIR"/..
 
 There are a handful of cases here that require renaming a module so it
 doesn't overlap with a stdlib module name. There are also some cycles
 here that we should still endeavor to fix, and some cycles will be
 hidden by deduplication algorithm in the cycle detector, so fixing
 these may expose other cycles.
 
   $ hg locate 'mercurial/**.py' 'hgext/**.py' | sed 's-\\-/-g' | python "$import_checker" -
   mercurial/dispatch.py mixed imports
      stdlib:    commands
      relative:  error, extensions, fancyopts, hg, hook, util
   mercurial/fileset.py mixed imports
      stdlib:    parser
      relative:  error, merge, util
   mercurial/revset.py mixed imports
      stdlib:    parser
      relative:  error, hbisect, phases, util
   mercurial/templater.py mixed imports
      stdlib:    parser
      relative:  config, error, templatefilters, templatekw, util
   mercurial/ui.py mixed imports
      stdlib:    formatter
      relative:  config, error, scmutil, util
   Import cycle: mercurial.cmdutil -> mercurial.context -> mercurial.subrepo -> mercurial.cmdutil
   Import cycle: hgext.largefiles.basestore -> hgext.largefiles.localstore -> hgext.largefiles.basestore
   Import cycle: mercurial.commands -> mercurial.commandserver -> mercurial.dispatch -> mercurial.commands