Remove patched ChatAnthropicVertex._format_output

In !59 (merged), we will introduce a monkey patch for a method in ChatAnthropicVertex

The original implementation for ChatAnthropicVertex._format_output could return a message that only has tool_calls populated but without content. This causes the following error message when calling Anthropic:

Error code: 400 - {'type': 'error', 'error': {'type': 'invalid_request_error', 'message': 'messages.16: `tool_result` block(s) provided when previous message does not contain any `tool_use` blocks'}}

To fix this, we've looked at the original implementation of ChatAnthropic._format_output, and patched the implementation we use.

We need to upstream these changes and upgrade langchain-google-vertexai to a version that contains the fix.