Simplified LCodeGen::GetNextEmittedBlock and LCodeGen::EmitGoto a bit.

GetNextEmittedBlock is always called with the same argument (an instance
variable), so let's remove it. In EmitGoto, avoid assignment to an argument.

This CL is split off another CL for easier reviewing.

Review URL: https://codereview.chromium.org/14246031

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14349 ce2b1a6d-e550-0410-aec6-3dcde31c8c00