[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>

docs/source/tutorials/features/long_sequence_context_parallel_multi_node.md

@@ -124,7 +124,6 @@ vllm serve /path_to_weight/DeepSeek-V3.1_w8a8mix_mtp \
   "kv_port": "30000",
   "engine_id": "0",
   "kv_connector_extra_config": {
-            "use_ascend_direct": true,
             "prefill": {
                     "dp_size": 1,
                     "tp_size": 16
@@ -192,7 +191,6 @@ vllm serve /path_to_weight/DeepSeek-V3.1_w8a8mix_mtp \
   "kv_port": "30000",
   "engine_id": "1",
   "kv_connector_extra_config": {
-            "use_ascend_direct": true,
             "prefill": {
                     "dp_size": 1,
                     "tp_size": 16

docs/source/tutorials/features/pd_colocated_mooncake_multi_instance.md

@@ -185,7 +185,6 @@ The template for the mooncake.json file is as follows:
     "metadata_server": "P2PHANDSHAKE",
     "protocol": "ascend",
     "device_name": "",
-    "use_ascend_direct": true,
     "master_server_address": "<your_server_ip>:50088",
     "global_segment_size": 107374182400
 }
@@ -195,7 +194,6 @@ The template for the mooncake.json file is as follows:
 | --------------| ------------------------| -----------------------------------|
 | metadata_server | P2PHANDSHAKE              | Point-to-point handshake mode  |
 | protocol              | ascend              | Ascend proprietary protocol    |
-| use_ascend_direct     | true                | Enable direct hardware access  |
 | master_server_address | 90.90.100.188:50088(for example) | Master server address|
 | global_segment_size   | 107374182400    | Size per segment (100 GB)      |