CLN: remove no-longer-needed object_compat

Author: jbrockmendel

pandas/core/arrays/string_arrow.py

@@ -278,7 +278,6 @@ def astype(self, dtype, copy: bool = True):
 
     # ------------------------------------------------------------------------
     # String methods interface
-    _object_compat = True
 
     _str_map = BaseStringArray._str_map
     _str_startswith = ArrowStringArrayMixin._str_startswith