Reduce the priority of debugging messages going to the console

These messages are in the normal (non-error) path and add to the
cout/cerr noise.

By default, `cfx run` has its output level set to `info` which
excludes the debug messages. To change this, set the
`extensions.sdk.console.logLevel` pref to `debug` or `all`.

https://developer.mozilla.org/Add-ons/SDK/Tools/console#Logging_Levels
Merge pull request #558 from fmarier/reduce_console_spam

Comment out debugging messages going to the console