Use a simply expanded variable for DIST_SOURCES and DIST_CFILES in Makefile.

This avoids a warning during 'make tarball' about csum-gcrypt.c being
specified twice as a source file.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
duperemove v0.09.beta3

Signed-off-by: Mark Fasheh <mfasheh@suse.de>