Translate attributes on system.xml files

[tzyganu]

It seams to me that the translate attribute on elements inside the system.xml files is useless and it should be removed.
From what I found in the code, the labels and comments are translated anyway in Magento\Backend\Model\Config\Structure\AbstractElement.
I also removed for test purposes the translate attribute from an element, change the translation for that text from the i18n folder and in the backend I got the translated version of the text.

[verklov]

@tzyganu, thanks for this ticket! I will consult the architect and get back to you once we have a response.

[vpelipenko]

Internal ticket: MAGETWO-28204

[piotrekkaminski]

We will be using an external tool to work on translations. We might then later push them to git or keep separate - not decided yet. Look for announcement soon.