Fix source after successful build
Closes: #1045435
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1045435
In the previous versions, mozc fails to build source after successful build. [1]
[1] https://wiki.debian.org/qa.debian.org/FTBFS/SourceAfterBuild
This commit fixes it by removing generated objects in debian/rules and ignore overridden contents with debian/source/options.
Edited by Kentaro Hayashi