Remove 'isJsonLogNoConn()' and 'isJsonLog()' JS helpers and simplify callers

The  isJsonLogNoConn() helper has a trivial implementation which always returns true. It looks like we can just delete this function after simplifying callers so that they no longer have code to handle the old logging format.

The story is similar for isJsonLog(). Its implementation runs the "buildinfo" command and returns true unless the version number is 4.2.x. In the master branch we are never testing against a 4.2.x version, so this function should always return true. We can simplify callers to assume that the logging format is the logv2 JSON format and then delete isJsonLog().