chore(extractor): remove duplicate MBID→Discogs map log line (#309)

The inner build_mbid_discogs_map_from_file function already logs
`📊 Built MBID→Discogs map: N entries from <path>` on completion
(jsonl_parser.rs:301). The caller's log added no new information.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: SimplicityGuy

extractor/src/extractor.rs

@@ -1126,7 +1126,6 @@ pub async fn process_musicbrainz_data(
     } else {
         HashMap::new()
     };
-    info!("📊 Built MBID→Discogs map: {} entries", artist_discogs_map.len());
 
     let mut record_counts: HashMap<String, u64> = HashMap::new();
     let mut success = true;