debugdeltachain: cleanup the double call to _slicechunk
Follow-up to Yuya's review on
43154a76f3927c4f0c8c6b02be80f0069c7d8fdb:
> Nit: hasattr() isn't necessary. revlog._slicechunk() is used in the previous
> block.
hasattr() isn't necessary indeed, as we are protected by the withsparseread
option, which was introduced at the same time as revlog._slicechunk, in
e2ad93bcc084b97c48f54c179365376edb702858.
And, as Yuya noticed, _slicechunk could be called only once.