main: Replace custom log function with console

console.log() is implemented with structured logging, and as we set an appropriate log domain, it's identical to the custom function bar the custom fields with extension data.

Few people know about those custom fields, and adding them comes at a cost, as we end up producing and parsing a stacktrace on every log() call.

It therefore seems appropriate to drop the custom function, and turn the global log() symbol into a simple convenience alias for console.log().

If it turns out that people do miss the custom fields, we can add an alternative to ExtensionUtils.