Tidy the "ripcip" argument into the visibility code

The "ripcip" argument of __wt_rec_update_select is a void * that's supposed to be either a WT_ROW * (rip) or WT_COL * (cip). It turns out that only the WT_ROW case is actually needed, so this can be simplified and made typesafe.

(There is one reference in the code that uses this value as a WT_COL, but it is (a) unreachable and also (b) wrong, so it can safely be removed.)