The background upload functionality is difficult to debug, since in cases like as in the parent issue, it is possible for the Sentry CLI to crash silently. Users may not notice that their debug files have not been uploaded.

Removing the background upload functionality likely will also simplify the Sentry CLI code.

Users who want to upload in the background can likely modify their shell script to call the Sentry CLI in the background. We should consider documenting how to do this.