fix exponential blowup when adding lots of identical files

fix exponential blowup when adding lots of identical files

This was an old problem when the files were being added unlocked,
so the changelog mentions that being fixed. However, recently it's also
affected locked files.

The fix for locked files is kind of stupidly simple. moveAnnex already
handles populating unlocked files, and only does it when the object file
was not already present. So remove the redundant populateUnlockedFiles
call. (That call was added all the way back in
cfaac52b88e157dd4e71626fe68af37015b9c9bd, and has always been
unncessary.)

Sponsored-by: Dartmouth College's Datalad project