cubicweb-vcsfile #5962570 [hgrepo] don't pass a revision to hg clone [validation pending]

[hgrepo] don't pass a revision to hg clone

It prevents hardlinking the repo's store to our cache, which makes the clone way slower on a big repo.

prioritynormal
typebug
done in2.2.0
load1.000
load left0.000
closed by#c5ae1c2472b7 [hgrepo] don't pass a revision to hg clone (closes #5962570)
patch[hgrepo] don't pass a revision to hg clone (closes #5962570) [applied][hgrepo] don't pass a revision to hg clone (closes #5962570) [applied]