remove os.environ[PATH] side effect from which

Author: tony

libtmux/common.py

@@ -384,7 +384,6 @@ def _is_executable_file_or_link(exe):
     for default_path in default_paths:
         if default_path not in search_path:
             search_path.append(default_path)
-    os.environ['PATH'] = os.pathsep.join(search_path)
     for path in search_path:
         full_path = os.path.join(path, exe)
         if _is_executable_file_or_link(full_path):