remove qwen3-next model file (#4573)

Let's remove qwen3-next model filecurrently. We'll support it later by
using vLLM origin model file

- vLLM version: v0.11.2
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

vllm_ascend/spec_decode/mtp_proposer.py

@@ -46,9 +46,7 @@ PADDING_SLOT_ID = -1
 
 _MTP_MODELS = {
     "DeepseekV3ForCausalLM":
-    ("vllm.model_executor.models.deepseek_mtp", "DeepSeekMTP"),
-    "Qwen3NextForCausalLM":
-    ("vllm_ascend.models.qwen3_next_mtp", "CustomQwen3NextMTP")
+    ("vllm.model_executor.models.deepseek_mtp", "DeepSeekMTP")
 }
 
 _DEFAULT_FIRST_LAYER = 'model.layers.0.self_attn.attn'