util: remove md5
This hash function is broken and should not be used by new code. It is
currently only used by keepalive.
% replace file with dir
initializing destination source-hg repository
scanning source...
sorting...
converting...
2 add d file
1 replace with d dir
0 add d/a
% manifest of tip
644 d/a
1 files updated, 0 files merged, 0 files removed, 0 files unresolved