Makefile: explicit_bzero.c was copied twice (GNU make gives a warning)

Makefile

@@ -36,7 +36,7 @@ dist: clean
 	@echo creating dist tarball
 	@mkdir -p slock-${VERSION}
 	@cp -R LICENSE Makefile README slock.1 config.mk \
-		${SRC} explicit_bzero.c config.def.h arg.h util.h slock-${VERSION}
+		${SRC} config.def.h arg.h util.h slock-${VERSION}
 	@tar -cf slock-${VERSION}.tar slock-${VERSION}
 	@gzip slock-${VERSION}.tar
 	@rm -rf slock-${VERSION}