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_tuple_positional/case.ww

@@ -0,0 +1,8 @@
+//ww:run-exit 42
+// Migrated from 700_e2e row 44.
+package main;
+fn pair() (i64, i64) = { return 10, 32; };
+fn main() i32 = {
+  let t: (i64, i64) = pair();
+  return (t.0 + t.1): i32;
+};