test: migrate 700_e2e rows to corpus fixtures; retire the carrier

136 rows migrated, 0 already owned, 3 wwstage-failing rows held out.

test/wcc/data/r700_divmod_multiret/case.ww

@@ -0,0 +1,8 @@
+//ww:run-exit 5
+// Migrated from 700_e2e row 5.
+package main;
+fn divmod(a: i64, b: i64) (i64, i64) = { return a / b, a % b; };
+fn main() i32 = {
+  let q, r = divmod(17, 5);
+  return (q + r): i32;
+};