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_fmt_println/case.ww

@@ -0,0 +1,11 @@
+//ww:run-exit 0
+// Migrated from 700_e2e row 25.
+package main;
+import fmt;
+import strconv;
+fn main() i32 = {
+  fmt.println("ww");
+  fmt.println(strconv.i64tos(42, strconv.base.DEC));
+  fmt.println(strconv.i64tos(-7, strconv.base.DEC));
+  return 0;
+};