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_def_str_write/case.ww

@@ -0,0 +1,9 @@
+//ww:run-exit 3
+// Migrated from 700_e2e row 112.
+package main;
+import os;
+def GREETING: str = "hi\n";
+fn main() i32 = {
+  os.write(1, GREETING.ptr, GREETING.len: u64);
+  return GREETING.len: i32;
+};