test(django): Drop span_streaming parametrize where the arm is inert (#7157)

### Description

These tests are event-only: they capture events, never spans, and the
`span_streaming` argument was only ever fed to `trace_lifecycle`. Both
arms exercised identical code paths and asserted identical payloads, so
the parametrize doubled the case count without adding coverage.

Tests that inspect spans or transactions keep their parametrize.

391 -> 356 cases.

Refs PY-2641
Refs #6975

Author: ericapisani