chore/ci: stop requiring unauthenticated SCIP uploads

Sourcegraph no longer accepts the workflow's GitHub token as upload authentication, so every push reports a failure after indexing succeeds. Keeping this upload would require a separately managed Sourcegraph access token; this repository does not otherwise need that credential, and comparable OSS repositories such as zoekt do not publish SCIP indexes from CI. Remove the obsolete workflow rather than leaving a permanently failing check or masking upload errors.

Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-019fb780-ec22-75e7-91a7-34c027582456

Author: keegancsmith