revert: computer-use cua-driver (PR #16919) (#16927)

Reverts PR #16919 (commits dad10a78d, 413ee1a28, b4a8031b2, afb958829)
which was merged prematurely. Restoring the pre-merge state so #14817
and #15328 can be revisited as standing PRs.

Reverted commits:
- afb958829 fix(computer-use): harden image-rejection fallback + AUTHOR_MAP
- b4a8031b2 fix(computer-use): unwrap _multimodal tool results
- 413ee1a28 feat(computer-use): background focus-safe backend
- dad10a78d feat(computer-use): cua-driver backend, universal any-model schema

Co-authored-by: teknium1 <teknium@users.noreply.github.com>

tools/computer_use_tool.py

@@ -1,39 +0,0 @@
-"""Shim for tool discovery. Registers `computer_use` with tools.registry.
-
-The real implementation lives in the `tools/computer_use/` package to keep
-the file structure clean. This shim exists because tools.registry auto-imports
-`tools/*.py` — we need a top-level module to trigger the registration.
-"""
-
-from __future__ import annotations
-
-from tools.computer_use.schema import COMPUTER_USE_SCHEMA
-from tools.computer_use.tool import (
-    check_computer_use_requirements,
-    handle_computer_use,
-    set_approval_callback,
-)
-from tools.registry import registry
-
-
-registry.register(
-    name="computer_use",
-    toolset="computer_use",
-    schema=COMPUTER_USE_SCHEMA,
-    handler=lambda args, **kw: handle_computer_use(args, **kw),
-    check_fn=check_computer_use_requirements,
-    requires_env=[],
-    description=(
-        "Universal macOS desktop control via cua-driver. Works with any "
-        "tool-capable model (Anthropic, OpenAI, OpenRouter, local vLLM, "
-        "etc.). Background computer-use: does NOT steal the user's cursor "
-        "or keyboard focus."
-    ),
-)
-
-
-__all__ = [
-    "handle_computer_use",
-    "set_approval_callback",
-    "check_computer_use_requirements",
-]