Remove unused file lru_cache.py

The LRUCache class originated in Dify v0.4, while later code primarily uses `from cachetools import LRUCache`.

api/core/helper/lru_cache.py

@@ -1,22 +0,0 @@
-from collections import OrderedDict
-from typing import Any
-
-
-class LRUCache:
-    def __init__(self, capacity: int):
-        self.cache: OrderedDict[Any, Any] = OrderedDict()
-        self.capacity = capacity
-
-    def get(self, key: Any) -> Any:
-        if key not in self.cache:
-            return None
-        else:
-            self.cache.move_to_end(key)  # move the key to the end of the OrderedDict
-            return self.cache[key]
-
-    def put(self, key: Any, value: Any) -> None:
-        if key in self.cache:
-            self.cache.move_to_end(key)
-        self.cache[key] = value
-        if len(self.cache) > self.capacity:
-            self.cache.popitem(last=False)  # pop the first item