[Doc][KV Pool]Revision KV Pool User Guide (#7434)

### What this PR does / why we need it?
Revise the KV Pool user guide:
1. Revise Mooncake environment variables and kvconnector extra configs.
2. Delete `use_ascend_direct` in kv connector extra config as it is
deprecated
3. Delete `kv_buffer_device` and `kv_rank` in P2P mooncake config
4. Unifies default `max-model-len` and `max-num-batch-tokens` in
examples given.

### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.17.0
- vLLM main:
4497431df6

---------

Signed-off-by: Pz1116 <zpbzpb123123@gmail.com>
Co-authored-by: Chao Lei <leichao139636@163.com>

tests/e2e/weekly/single_node/models/test_qwen3_30b_acc.py

@@ -45,7 +45,6 @@ mooncake_json = {
     "metadata_server": "P2PHANDSHAKE",
     "protocol": "ascend",
     "device_name": "",
-    "use_ascend_direct": True,
     "master_server_address": "",
     "global_segment_size": 30000000000
 }