Remove dangling ego_frames/ego_preview Data Studio configs

These two config_name entries in the YAML frontmatter pointed at manifest/ego_frames_v1.parquet and preview/ego_preview.parquet -- both were the stale June-era single-pilot-scene files deleted earlier in this cycle, so the Dataset Viewer was 404ing trying to build the subset dropdown for them. multi_object, mos_phase_preview, and single_object configs were verified to still point at real, existing files and are untouched. A real ego preview table (matching mos_phase_preview's pattern) is planned as a follow-up commit.

README.md

@@ -37,16 +37,6 @@ configs:
   data_files:
   - split: "preview"
     path: "preview/mos_phase_preview.parquet"
-- config_name: ego_frames
-  description: "Frame-level manifest rows for optional egocentric MOS views. Ego does not contribute to ESD."
-  data_files:
-  - split: "ego"
-    path: "manifest/ego_frames_v1.parquet"
-- config_name: ego_preview
-  description: "Data Studio media table for egocentric MOS RGB/depth/mask/fisheye previews."
-  data_files:
-  - split: "preview"
-    path: "preview/ego_preview.parquet"
 - config_name: single_object
   description: "SOS selected-object catalog; one 360 collection per object, no difficulty split."
   data_files: