[refactor] refactor deepseek-related files (#2849)

### What this PR does / why we need it?
This PR deletes ~2K lines of code about deepseek modeling. It falls back
CustomDeepseekV2 modules to original vllm implementations and adapts
some modifications in vllm about deepseek and moe.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
E2E  vllm serving with torchair graph mode and eager mode.

- vLLM version: v0.10.2
- vLLM main:
759ef49b15

---------

Signed-off-by: linfeng-yuan <1102311262@qq.com>
Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>
Co-authored-by: yiz-liu <136800916+yiz-liu@users.noreply.github.com>
Co-authored-by: Yizhou Liu <liu_yizhou@outlook.com>

tests/ut/test_platform.py

@@ -36,6 +36,7 @@ class TestNPUPlatform(TestBase):
         mock_ascend_config = MagicMock()
         mock_ascend_config.torchair_graph_config.enabled = False
         mock_ascend_config.ascend_scheduler_config.enabled = False
+        mock_ascend_config.enable_shared_expert_dp = False
         return mock_ascend_config
 
     def setUp(self):
@@ -479,6 +480,7 @@ class TestNPUPlatform(TestBase):
     def test_get_attn_backend_cls_use_v1_and_mla(self, mock_get_ascend_config):
         mock_config = MagicMock()
         mock_config.torchair_graph_config.enabled = False
+        mock_config.enable_shared_expert_dp = False
 
         mock_get_ascend_config.return_value = mock_config