[Refactor][EAGLE] 8/N delete mtp_proposer (#7016)

### What this PR does / why we need it?
This PR aims to delete mtp_proposer. By fixing a bug in both dsv32 and
glm5, now it should be ok to remove mtp_proposer. The bug is actually
about unnecessary slicing of `slot_mapping`.

### Does this PR introduce _any_ user-facing change?
N/A

### How was this patch tested?
by ci

- vLLM version: v0.16.0
- vLLM main:
15d76f74e2

---------

Signed-off-by: Zetong Li <slippersss@126.com>

vllm_ascend/attention/attention_v1.py

@@ -324,7 +324,11 @@ class AscendAttentionMetadataBuilder(AttentionMetadataBuilder[AscendMetadata]):
         common_attn_metadata: AscendCommonAttentionMetadata,
         attn_state: AscendAttentionState = AscendAttentionState.DecodeOnly,
     ):
-        if attn_state in (AscendAttentionState.DecodeOnly, AscendAttentionState.ChunkedPrefill):
+        if attn_state in (
+            AscendAttentionState.DecodeOnly,
+            AscendAttentionState.ChunkedPrefill,
+            AscendAttentionState.SpecDecoding,
+        ):
             attn_metadata = self.build(
                 common_prefix_len=0,
                 common_attn_metadata=common_attn_metadata,