deferred_style: use bz2 and zlib module instead of python2 only syntax

bt5/erp5_deferred_style/SkinTemplateItem/portal_skins/erp5_deferred_style_core/Base_renderReportSection.py

+import bz2
 request = container.REQUEST
 request.form.update(report_request)
 request.other.update(report_request)
@@ -25,4 +26,4 @@ with portal.Localizer.translationContext(localizer_language):
 
   report_section.popReport(portal, render_prefix=render_prefix)
 
-return report_section_idx, data.encode('utf8').encode('bz2')
+return report_section_idx, bz2.compress(data.encode('utf8'))

bt5/erp5_deferred_style/SkinTemplateItem/portal_skins/erp5_deferred_style_core/Base_report.py

 # pylint: disable=redefined-builtin
+import bz2
+import zlib
 
 request = container.REQUEST
 request.form.update(report_request)
@@ -21,9 +23,9 @@ with portal.Localizer.translationContext(localizer_language):
   def decodeReportSection(data):
     # BBB We use to encode in zlib
     try:
-      return data.decode('bz2')
+      return bz2.decompress(data)
     except IOError:
-      return data.decode('zlib')
+      return zlib.decompress(data)
   if portal.portal_preferences.getPreferredDeferredReportStoredAsDocument():
     pt_render_format = None
   else: