[legacy] clean up legacy code (#4743)

* [legacy] remove outdated codes of pipeline (#4692)

* [legacy] remove cli of benchmark and update optim (#4690)

* [legacy] remove cli of benchmark and update optim

* [doc] fix cli doc test

* [legacy] fix engine clip grad norm

* [legacy] remove outdated colo tensor (#4694)

* [legacy] remove outdated colo tensor

* [test] fix test import

* [legacy] move outdated zero to legacy (#4696)

* [legacy] clean up utils (#4700)

* [legacy] clean up utils

* [example] update examples

* [legacy] clean up amp

* [legacy] fix amp module

* [legacy] clean up gpc (#4742)

* [legacy] clean up context

* [legacy] clean core, constants and global vars

* [legacy] refactor initialize

* [example] fix examples ci

* [example] fix examples ci

* [legacy] fix tests

* [example] fix gpt example

* [example] fix examples ci

* [devops] fix ci installation

* [example] fix examples ci

examples/language/gpt/titans/model/gpt1d.py

@@ -9,13 +9,13 @@ from torch import nn as nn
 
 from colossalai import kernel
 from colossalai import nn as col_nn
-from colossalai.core import global_context as gpc
 from colossalai.kernel.cuda_native.scaled_softmax import AttnMaskType
+from colossalai.legacy.core import global_context as gpc
 from colossalai.legacy.nn.layer import Linear1D_Col, Linear1D_Row
 from colossalai.legacy.nn.layer.base_layer import ParallelLayer
 from colossalai.legacy.nn.layer.utils import ACT2FN, divide
+from colossalai.legacy.utils.activation_checkpoint import checkpoint
 from colossalai.utils import checkpoint
-from colossalai.utils.activation_checkpoint import checkpoint
 
 __all__ = [
     'GPTMLP1D', 'GPTSelfAttention1D', 'GPTTransformerLayer1D', 'FusedGPTSelfAttention1D', 'FusedGPTTransformerLayer1D'