Remove CompilationInfoWithZone from public API.

Remove CompilationInfoWithZone from public API.

This removes the CompilationInfoWithZone class from the header file
because it is more than a pure convenience class and shouldn't be used
outside of the compiler at all.

R=titzer@chromium.org

Review URL: https://codereview.chromium.org/1000353004

Cr-Commit-Position: refs/heads/master@{#27411}