Remove 28M model

Project/Assets/ML-Agents/Examples/Worm/TFModels/WormDynamic28M.nn.meta

-fileFormatVersion: 2
-guid: e5fd6fc6be11c49b49542716a40d3ddc
-ScriptedImporter:
-  fileIDToRecycleName:
-    11400000: main obj
-    11400002: model data
-  externalObjects: {}
-  userData: 
-  assetBundleName: 
-  assetBundleVariant: 
-  script: {fileID: 11500000, guid: 19ed1486aa27d4903b34839f37b8f69f, type: 3}