AtlasPyFwdBwdPorts: remove enum34 module

enum34 is provided by LCG_95 now.

External/AtlasPyFwdBwdPorts/CMakeLists.txt

-# $Id: CMakeLists.txt 790212 2016-12-16 17:43:15Z ssnyder $
 
 # The name of the package:
 atlas_subdir( AtlasPyFwdBwdPorts )
@@ -101,13 +100,7 @@ _setup_python_package( pyflakes
 _setup_python_package( flake8
    ${CMAKE_CURRENT_SOURCE_DIR}/src/flake8-3.6.0.tar.gz
    178485aed0799655d0cbf2e3bdcfaddc
-   DEPENDS pyflakes pycodestyle mccabe enum34
-   SINGLE_VERSION )
-
-# Install enum34:
-_setup_python_package( enum34
-   ${CMAKE_CURRENT_SOURCE_DIR}/src/enum34-1.1.6.tar.gz
-   5f13a0841a61f7fc295c514490d120d0
+   DEPENDS pyflakes pycodestyle mccabe
    SINGLE_VERSION )
 
 # Install mccabe: