Revert "libcutils: remove unused "jstring.h"."

This reverts commit aa96e8898ce44116aa6b5b459b38db77db8bd903.

Reason for revert: It caused BB, and b/139257138 is for your reference

Change-Id: I93f1d0ba0fa43325e2815e9b2de84bb7cb41c457
4 files changed