Revert addition of extendedness column to imsim

This was inadvertently merged.

python/lsst/sdm_schemas/schemas/imsim.yaml

@@ -8092,13 +8092,13 @@ tables:
     datatype: boolean
     description: This flag is set if a trailed source contains edge pixels.
     fits:tunit:
-  - name: extendedness
-    "@id": "#DiaSource.extendedness"
-    datatype: double
-    description: A measure of extendedness, computed by comparing an object's moment-based traced radius to
-      the PSF moments. extendedness = 1 implies a high degree of confidence
-      that the source is extended. extendedness = 0 implies a high degree of confidence
-      that the source is point-like.
+  # - name: extendedness
+  #  "@id": "#DiaSource.extendedness"
+  #  datatype: double
+  #  description: A measure of extendedness, computed by comparing an object's moment-based traced radius to
+  #    the PSF moments. extendedness = 1 implies a high degree of confidence
+  #    that the source is extended. extendedness = 0 implies a high degree of confidence
+  #    that the source is point-like.
 - name: ForcedSourceOnDiaObject
   "@id": "#ForcedSourceOnDiaObject"
   description: this is forcedSourceOnDiaObjectTable_tract in the butler repo