Add more dependencies. Remove function from yamato_utils.py that was only used for inferece tests.

com.unity.ml-agents/package.json

   "unity": "2018.4",
   "description": "Use state-of-the-art machine learning to create intelligent character behaviors in any Unity environment (games, robotics, film, etc.).",
   "dependencies": {
-      "com.unity.barracuda": "1.0.2",
-      "com.unity.modules.physics2d": "1.0.0",
-      "com.unity.modules.imageconversion": "1.0.0"
+    "com.unity.barracuda": "1.0.2",
+    "com.unity.modules.imageconversion": "1.0.0",
+    "com.unity.modules.jsonserialize": "1.0.0",
+    "com.unity.modules.physics": "1.0.0",
+    "com.unity.modules.physics2d": "1.0.0"
   }
 }

ml-agents/tests/yamato/yamato_utils.py

     return res.returncode
 
 
-def find_executables(root_dir: str) -> List[str]:
-    """
-    Try to find the player executable. This seems to vary between Unity versions.
-    """
-    ignored_extension = frozenset([".dll", ".dylib", ".bundle"])
-    ignored_files = frozenset(["macblas"])
-    exes = []
-    for root, _, files in os.walk(root_dir):
-        for filename in files:
-            file_root, ext = os.path.splitext(filename)
-            if ext in ignored_extension or filename in ignored_files:
-                continue
-            file_path = os.path.join(root, filename)
-            if os.access(file_path, os.X_OK):
-                exes.append(file_path)
-    return exes
-
-
 def init_venv(
     mlagents_python_version: str = None, extra_packages: Optional[List[str]] = None
 ) -> str: