Remove unnecessary validation for local global attention (#12049)

Since `local_global_attention` is [already an int
list](https://github.com/pytorch/executorch/blob/main/extension/llm/export/config/llm_config.py#L165),
this validation doesn't make any sense to do.

Author: jackzhxng

extension/llm/export/config/llm_config.py

@@ -18,7 +18,6 @@
 """
 
 import argparse
-import ast
 import re
 from dataclasses import dataclass, field
 from enum import Enum
@@ -166,7 +165,6 @@ class ModelConfig:
 
     def __post_init__(self):
         self._validate_attention_sink()
-        self._validate_local_global_attention()
 
         if self.quantize_kv_cache and not self.use_kv_cache:
             raise ValueError(
@@ -186,18 +184,6 @@ def _validate_attention_sink(self):
                     "The value of use_attention_sink must be structured like '<sink_size>,<window_size>,<batch_eviction_size>'"
                 )
 
-    def _validate_local_global_attention(self):
-        if self.local_global_attention:
-            local_global_err = "The value of local_global_attention must be a list of integers, e.g., [0, 16, 0, 16]"
-            try:
-                parsed = ast.literal_eval(self.local_global_attention)
-                if not (
-                    isinstance(parsed, list) and all(isinstance(i, int) for i in parsed)
-                ):
-                    raise ValueError(local_global_err)
-            except Exception:
-                raise ValueError(local_global_err)
-
 
 ################################################################################
 ################################ ExportConfig ##################################