Remove warning messages (microsoft#2151)

Remove a couple of warning messages in onnxscript that hasn't been
useful so far and is typically a distraction.

Author: gramalingam

onnxscript/converter.py

@@ -942,7 +942,6 @@ def _translate_callee_expr(self, node: ast.AST) -> values.Op:  # pylint: disable
             opname = node.attr
             if opname in module:
                 return values.Op(module, node.attr)
-            warn(f"'{opname}' is not a known op in '{module}'")
             return values.Op(module, node.attr)
         if isinstance(node, ast.Name):
             function_name = node.id

onnxscript/values.py

@@ -109,8 +109,6 @@ def __getattr__(self, attr: str):
             raise AttributeError(f"Attribute {attr} not found.") from exc
 
     def add_function_def(self, fun):
-        if fun.name in self.function_defs:
-            logger.warning("%s: Already defined.", fun.name)
         self.function_defs[fun.name] = fun
 
     def _prepare_inputs(self, _: onnx.defs.OpSchema, *inputs):