vm-update-draft-count called too often

[Uday Reddy]

The function `vm-update-draft-count' is currently called every time `vm-update-summary-and-mode-line' is called. This is clearly an overkill, because the draft-count is only affected when `vm-postpone-message' is run.

Can we get rid of the call to `vm-update-draft-count' in `vm-update-summary-and-mode-line'?

(This was introduced in rev. 498, with the tag line "Fixed updating of composition and draft count".)