[MCP] Don't require experimental_use_rmcp_client for no-auth http servers (#4689)

The `experimental_use_rmcp_client` flag is still useful to:
1. Toggle between stdio clients
2. Enable oauth beacuse we want to land
https://github.com/modelcontextprotocol/rust-sdk/pull/469,
https://github.com/openai/codex/pull/4677, and binary signing before we
enable it by default

However, for no-auth http servers, there is only one option so we don't
need the flag and it seems to be working pretty well.

codex-rs/core/src/mcp_connection_manager.rs

@@ -108,9 +108,6 @@ impl McpClientAdapter {
         params: mcp_types::InitializeRequestParams,
         startup_timeout: Duration,
     ) -> Result<Self> {
-        info!(
-            "new_stdio_client use_rmcp_client: {use_rmcp_client} program: {program:?} args: {args:?} env: {env:?} params: {params:?} startup_timeout: {startup_timeout:?}"
-        );
         if use_rmcp_client {
             let client = Arc::new(RmcpClient::new_stdio_client(program, args, env).await?);
             client.initialize(params, Some(startup_timeout)).await?;
@@ -205,17 +202,6 @@ impl McpConnectionManager {
                 continue;
             }
 
-            if matches!(
-                cfg.transport,
-                McpServerTransportConfig::StreamableHttp { .. }
-            ) && !use_rmcp_client
-            {
-                info!(
-                    "skipping MCP server `{server_name}` because the legacy MCP client only supports stdio servers",
-                );
-                continue;
-            }
-
             let startup_timeout = cfg.startup_timeout_sec.unwrap_or(DEFAULT_STARTUP_TIMEOUT);
             let tool_timeout = cfg.tool_timeout_sec.unwrap_or(DEFAULT_TOOL_TIMEOUT);