Stop modifying locale before sending to Google Translate

[jqr]

In #292 the from/to locales were modified to be limited to just the language portion of a locale tag except if it was within one of the listed set of langague-REGION tags. This was to fix #286.

That change no longer seems to be required by the underlying API:

EasyTranslate.translate("horse", to: "es")       # => "caballo"
EasyTranslate.translate("horse", to: "es-es")    # => "caballo"
EasyTranslate.translate("horse", to: "es-ES")    # => "caballo"

EasyTranslate.translate("caballo", to: "en")     # => "horse"
EasyTranslate.translate("caballo", to: "en-us")  # => "horse"
EasyTranslate.translate("caballo", to: "en-US")  # => "horse"

And maintaining that list directly in code causes several small issues, #555 #556, and #557 which actually is translating things into the incorrect language altogether.

Given that, it seems worthy of removing the vestigial locale modification code entirely and just relying on new improved behavior of the Google Translate API and EasyTranslate.

[glebm]

Thanks!