Test always evaluates the same

Defect 114049 (STATIC_C)
Checker DEADCODE (subcategory redundant_test)
File: /src/btree/bt_curnext.c
Function __cursor_row_next
/src/btree/bt_curnext.c, line: 403
At condition "upd != NULL", the value of "upd" cannot be "NULL".

            if (upd != NULL && upd->type == WT_UPDATE_TOMBSTONE) {

/src/btree/bt_curnext.c, line: 401
Condition "upd == NULL", taking false branch. Now the value of "upd" is not "NULL".

            if (upd == NULL)

/src/btree/bt_curnext.c, line: 403
The condition "upd != NULL" must be true.

            if (upd != NULL && upd->type == WT_UPDATE_TOMBSTONE) {