Remove `designate` for `rewriteLeaf` in merge.
Remove `designate` for `rewriteLeaf` in merge.

Remove the call to `designate` to obtain a key for `rewriteLeaf` in the
`mergeLeaves` function. The `rewriteLeaf` function no longer accepts a
key argument. It will read the key from the leaf page.

See #192.
See #189.

cesarmarinhorj/strata,bigeasy/strata,bigeasy/strata,cesarmarinhorj/strata