Update SettingsGeneralActivity.java

Reverted back the Unit changes so it will be possible to select it independendtly from Driving region:

https://code.google.com/p/osmand/issues/detail?id=2317
https://groups.google.com/forum/#!topic/osmand/9P6FclWSyw8
Merge pull request #639 from vrtareg/master

Update SettingsGeneralActivity.java