Remove core MCP list tools op (#21281)

## Why

The core `Op::ListMcpTools` request path is no longer needed. Keeping it
around left a dead request/response surface alongside the app-server MCP
inventory APIs that own current server status listing.

## What Changed

- Removed `Op::ListMcpTools`, `EventMsg::McpListToolsResponse`, and the
core handler that built the MCP snapshot response.
- Removed the now-unused `codex-mcp` snapshot wrapper/export and passive
event handling arms in rollout and MCP-server consumers.
- Updated tests that used the old op as a synchronization hook to wait
on existing startup/skills events, and deleted the plugin test that only
exercised the removed listing op.

## Validation

- `cargo test -p codex-protocol`
- `cargo test -p codex-mcp`
- `cargo test -p codex-rollout -p codex-rollout-trace -p
codex-mcp-server`
- `cargo test -p codex-core --test all
pending_input::queued_inter_agent_mail`
- `cargo test -p codex-core --test all
rmcp_client::stdio_mcp_tool_call_includes_sandbox_state_meta`
- `cargo test -p codex-core --test all
rmcp_client::stdio_image_responses`
- `just fix -p codex-core -p codex-protocol -p codex-mcp -p
codex-rollout -p codex-rollout-trace -p codex-mcp-server`

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -334,7 +334,6 @@ async fn run_codex_tool_session_inner(
                     | EventMsg::AgentReasoningSectionBreak(_)
                     | EventMsg::McpToolCallBegin(_)
                     | EventMsg::McpToolCallEnd(_)
-                    | EventMsg::McpListToolsResponse(_)
                     | EventMsg::RealtimeConversationListVoicesResponse(_)
                     | EventMsg::ExecCommandBegin(_)
                     | EventMsg::TerminalInteraction(_)