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_mul_locals/case.ww

@@ -0,0 +1,8 @@
+//ww:run-exit 42
+// Migrated from 700_e2e row 4.
+package main;
+fn main() i32 = {
+  let a: i32 = 6;
+  let b: i32 = 7;
+  return a * b;
+};