[Fixbug] Clear the intermediate object files for kernel tuning (#339)

This PR clears the intermediate object files generated during tuning.

This should reduce 2/3 cache size without hurting any functionality. 

#338

python/hidet/drivers/build_task.py

@@ -13,6 +13,7 @@
 import re
 import os
 import json
+import shutil
 from hashlib import sha256
 from typing import List, Optional, Tuple
 
@@ -162,6 +163,10 @@ def launch(arg: meta.types(param_types)):
     # build task ir module
     build_ir_module(ir_module=task_ir_module, output_dir=task_dir, output_kind='.so', target=target)
 
+    # clear the candidate object files that are no longer needed
+    if not hidet.option.get_option('debug_cache_tuning'):
+        shutil.rmtree(os.path.join(task_dir, 'candidates'), ignore_errors=True)
+
 
 def generate_meta_data(task: Task, task_dir: str, build_target: str, num_candidates: int):
     from hidet.ir.compute import TensorNode