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_match_default_arm/case.ww

@@ -0,0 +1,15 @@
+//ww:run-exit 7
+// Migrated from 700_e2e row 54.
+package main;
+fn parse(n: i64) (i64 | i32) = {
+  if (n < 0) { return 1: i32; };
+  return n;
+};
+fn main() i32 = {
+  let r: (i64 | i32) = parse(-1);
+  match (r) {
+    case let v: i64 => return 1;
+    case => return 7;
+  };
+  return 0;
+};