Don't inline the Avro logo in the navbar for 1.11.1

If we change the Avro logo (AVRO-3554), we probably don't want to inline it for the navbar of the new website.

It should be located at a common location (such as the current https://avro.apache.org/images/avro-logo.png) or at a version specific location, (such as the current https://avro.apache.org/docs/1.11.0/images/avro-logo.png)