[Bugfix][SHM] Use writer lock by default and remove redundant env (#4117)

### What this PR does / why we need it?
This PR aims to remove env introduced by #3988 and use lock by default.
As described in vllm-project/vllm#27858, we
have tested the writer lock method in various scenarios and the
performance is almost unaffected. Therefore, we believe that it would be
safe to enable the lock by default and remove the redundant env
`SHM_BARRIER` now.

After discussion, we decide to preserve env and set it as true by
default.

### Does this PR introduce _any_ user-facing change?
`SHM_BARRIER` is set as true by default.

### How was this patch tested?
by ci

---------

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

Author: slippersss

vllm_ascend/patch/platform/__init__.py

@@ -25,6 +25,6 @@
         "EXPERT_MAP_RECORD", "false") == "true":
     import vllm_ascend.patch.platform.patch_multiproc_executor  # noqa
 
-if os.getenv("SHM_BARRIER", "false") == "true":
+if os.getenv("SHM_BARRIER", "true") == "true":
     import vllm_ascend.patch.platform.patch_core  # noqa
     import vllm_ascend.patch.platform.patch_message_queue  # noqa

vllm_ascend/patch/worker/__init__.py

@@ -15,6 +15,8 @@
 # limitations under the License.
 #
 
+import os
+
 from vllm.triton_utils import HAS_TRITON
 
 if HAS_TRITON:
@@ -29,4 +31,7 @@
 import vllm_ascend.patch.worker.patch_multimodal_merge  # noqa
 import vllm_ascend.patch.worker.patch_minicpm  # noqa
 import vllm_ascend.patch.worker.patch_deepseek_mtp  # noqa
-import vllm_ascend.patch.worker.patch_attention_layer  # noqa
+import vllm_ascend.patch.worker.patch_attention_layer  # noqa
+
+if os.getenv("SHM_BARRIER", "true") == "true":
+    import vllm_ascend.patch.platform.patch_message_queue  # noqa