Remove a stray screen dump, and stop CTREE_DUMP=1 creating one

`CTREE_DUMP=1` is the obvious thing to type, and the test wrote the dump to a
file named `1` in the repo root — where `git add -A` swept it into the previous
commit. A value without a path separator now goes to the temp dir and says where.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VkCWU9Ab6wYHmTke8vuVMv

Author: claude