These thin wrappers around _capture_log_snapshot had zero production
callers after the snapshot refactor — run_debug_share uses snapshots
directly and collect_debug_report captures internally. The wrappers
also caused a performance regression: _read_log_tail read up to 512KB
and built full_text just to return tail_text.
Remove both wrappers and migrate TestReadFullLog → TestCaptureLogSnapshot
to test _capture_log_snapshot directly. Same coverage, tests the real
API instead of dead indirection.