Simplify .travis.yml

- Remove clang for now (doesn't work)
- Simplify script to stay below the time limit
Removed wrong line in .travis.yml
Remove pcl_2d and dependent files
Remove pcl_cuda
Remove pcl_gpu
Remove CUDA related cmake stuff
Remove pcl_ml and dependent files
Remove pcl_simulation
Remove pcl_stereo
Remove 3rdparty stuff
Remove SSE and change -O4 to -O2
Testing again, maybe we don't hit the 50 minutes
Remove unused parameters in geometry
Remove unused variables in search
Fix unused variables in registration
Fixed unused variables in io
Fix union warning in octree