In Android framework, make tools depend on jsoncpp

Always build the tools with JSON, but either build our own
or use the system's.

Rename skia_build_json_writer to skia_use_system_jsoncpp,
since we now always build with JSON.

Remove SK_BUILD_JSON_WRITER, which was only there so
we could build without JSON it in the framework.

BUG=skia:2448
R=djsollen@google.com, reed@google.com

Author: scroggo@google.com

Review URL: https://codereview.chromium.org/303913002
16 files changed