[Extensions Schema Compiler] Clean up json_schema_api.gni

Do some quick clean up of json_schema_compiler.gni before splitting
it out into multiple targets.
- Remove ineffective visibility assignments and update docs
- Remove stale references (generate_static_library) and unused
  options (output_name).

Bug: 864576
Change-Id: I395bfcc0f222cfdae269f222a7b4d28e2fcdeed9
Reviewed-on: https://chromium-review.googlesource.com/1140504
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578098}
1 file changed