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>

tests/tools/test_registry.py

@@ -296,7 +296,6 @@ class TestBuiltinDiscovery:
             "tools.browser_tool",
             "tools.clarify_tool",
             "tools.code_execution_tool",
-            "tools.computer_use_tool",
             "tools.cronjob_tools",
             "tools.delegate_tool",
             "tools.discord_tool",