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_try_prop/case.ww

@@ -0,0 +1,20 @@
+//ww:run-exit 99
+// Migrated from 700_e2e row 49.
+package main;
+fn try1(n: i64) (i64 | i32) = {
+  if (n < 0) { return 99: i32; };
+  return n;
+};
+fn try2(n: i64) (i64 | i32) = {
+  let v: i64 = try1(n)?;
+  return v + 100;
+};
+fn main() i32 = {
+  let r: (i64 | i32) = try2(-1);
+  let s: i64 = 0;
+  match (r) {
+    case let v: i64 => s = v;
+    case let e: i32 => s = e: i64;
+  };
+  return s: i32;
+};