Disable log tag for production

The prefix breaks the output from Lograge and we are specifying the request id already. [1]
Also moving the stdout as default to application.rb so that it applies to all environments, without needing the env var as we are removing that.

[1]: #369 (comment)

Author: chao-xian

config/environments/production.rb

@@ -54,7 +54,7 @@
   # config.log_tags = [:request_id]
 
   # Prepend all log lines with the following tags.
-  config.log_tags = [:request_id]
+  # config.log_tags = [:request_id]
 
   # Info include generic and useful information about system operation, but avoids logging too much
   # information to avoid inadvertent exposure of personally identifiable information (PII). If you