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_str_eq/case.ww

@@ -0,0 +1,12 @@
+//ww:run-exit 30
+// Migrated from 700_e2e row 27.
+package main;
+fn main() i32 = {
+  let a: str = "hello";
+  let b: str = "hello";
+  let c: str = "world";
+  let n: i32 = 0;
+  if (a == b) { n += 10; };
+  if (a != c) { n += 20; };
+  return n;
+};