Reduce duplicate broadcasting done when pasting a range of cells from clip.

We do pasting from clip in 2 steps: 1) delete the destination range, then
2) paste the content onto the destination range.  The old code would broadcast
both during 1) and 2).  This change consolidates them and do broadcasting
only once at the end, and also avoids broadcasting the same cell twice,
which the old code sometimes did.

Change-Id: Ic524c2b70888ce158619d99cbfb55dea85870497