[keyserver] Deprecate streamJSON
Summary:
The only usages of this function were removed in D9145. Removing it from the codebase allows us to rip out three NPM packages.
Depends on D10165
Test Plan: Flow
Reviewers: michal, kamil
Reviewed By: kamil
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D10166