And removing unused code.
- tarsum.go :
NewTarSumHash could be non exported (for now)
NewTarSumForLabel is never used, except for the tests
- fileinfosums.go:
SortByPos is never used, except for the tests
- versionning.go:
GetVersions is never used, expect for the tests
Signed-off-by: Vincent Demeester <vincent@sbr.pm>
