Fix shouldTranslate() for Optimize translations

Summary: We used to allow Optimize translations regardless of the
Eval.JitAMaxUsage limit, but I recently broke that while refactoring
the code to use shouldTranslate() to also check the
Eval.JitGlobalTranslationLimit limit.  This diff fixes the issue.

Reviewed By: @swtaarrs

Differential Revision: D1604752