Removed serbian translation for 2.0, too

Refs https://github.com/cakephp/docs/pull/1948

Turns out the serbian translation isn't kept up to date for 2.0 either.
No wonder when the initial maintainer  "Aleksa-Savic" disappeared.

The commits in this tree are not many:
https://github.com/cakephp/docs/commits/master/sr
Removed romanian translation for 2.0, too

Refs https://github.com/cakephp/docs/pull/1948

The Romanian translation was started but not kept up to date for quite some time now:

The commits in this tree are not many:
https://github.com/cakephp/docs/commits/master/ro
Merge pull request #1949 from cakephp/2.0-serbian-removal

Removed serbian translation for 2.0, too
Merge pull request #1950 from cakephp/2.0-romanian-removal

Removed romanian translation for 2.0, too