Duplicated entries in conffiles file

[robertauer]

If the debian package has been built already and is built again, the entries in the conffiles file are written to it twice. This leads to the following lintian error:

E: ces-commons: duplicate-conffile FILENAME
N: 
N:    The file is listed more than once in your debian/conffiles file.
N:    Usually, this is because debhelper (dh_installdeb, compat level 3 or
N:    higher) will add any files in your package located in /etc automatically
N:    to the list of conffiles, so if you do that manually too, you'll get
N:    duplicates.
N:    
N:    Severity: important, Certainty: certain
N:    
N:    Check: conffiles, Type: binary

This most likely is caused by the $(CONFFILES_FILE_TMP) file not being removed after usage.