Remove unused/broken configurations from Travis CI
Remove unused/broken configurations from Travis CI

LLVM 4 is not supported anymore, and the Clang build on Mac OS X
seems broken because of unknown compiler flag.

Oblomov/pocl,pocl/pocl,pocl/pocl,franz/pocl,pocl/pocl,Oblomov/pocl,franz/pocl,Oblomov/pocl,Oblomov/pocl,franz/pocl,pocl/pocl,pocl/pocl,franz/pocl,franz/pocl,Oblomov/pocl