CONFIG: sourcing etc/cshrc twice unset the environment (fixes #2458)

etc/config.csh/setup

@@ -5,7 +5,7 @@
 #   \\  /    A nd           | www.openfoam.com
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
-#     Copyright (C) 2018-2021 OpenCFD Ltd.
+#     Copyright (C) 2018-2022 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -210,8 +210,8 @@ endif
 
 # Remove duplicates from environment paths
 
-_foamClean PATH "$foamOldDirs"
-_foamClean MANPATH "$foamOldDirs"
+_foamClean PATH
+_foamClean MANPATH
 _foamClean -lib
 
 # Add trailing ':' for system manpages