twitter-server: Remove -Xfatal-warnings scalac option
twitter-server: Remove -Xfatal-warnings scalac option

Problem

This option is too aggressive and causes issues with warnings
from scaladoc generation.

Resolution

Remove the option for now.

RB_ID=796979

twitter/twitter-server,twitter/twitter-server,BuoyantIO/twitter-server,BuoyantIO/twitter-server,BuoyantIO/twitter-server,twitter/twitter-server,BuoyantIO/twitter-server