Improve code quality based on DeepSource (#299)

DeepSource identified:
Method '_table_exists_in_db' is abstract in class 'SqlDecoratedOperator' but is not overridden
Method 'handle_dataframe_func' is abstract in class 'SqlDecoratedOperator' but is not overridden

In several subclasses, as part of:
https://deepsource.io/gh/astro-projects/astro/run/99bc601f-513a-4dbc-b771-65cf795aa2aa/python/PYL-W0223

src/astro/sql/operators/sql_decorator.py

@@ -246,9 +246,6 @@ def clean_trailing_semicolon(query):
             statement = f"CREATE TABLE {output_table_name} AS ({clean_trailing_semicolon(query)});"
         return statement
 
-    def handle_dataframe_func(self, input_table):
-        raise NotImplementedError("Need to add dataframe func to class")
-
     @provide_session
     def pre_execute(self, context, session=None):
         """This hook is triggered right before self.execute() is called."""
@@ -260,10 +257,6 @@ def post_execute(self, context, result=None):
         """
         pass
 
-    def _table_exists_in_db(self, conn: str, table_name: str):
-        """Override this method to enable sensing db."""
-        raise NotImplementedError("Add _table_exists_in_db method to class")
-
     def _process_params(self):
         if self.conn_type == "snowflake":
             self.parameters = snowflake_transform.process_params(

src/astro/sql/parsers/sql_directory_parser.py

@@ -218,12 +218,6 @@ def find_templated_fields(file_string):
 class ParsedSqlOperator(SqlDecoratedOperator):
     template_fields = ("parameters",)
 
-    def _table_exists_in_db(self, conn: str, table_name: str):
-        pass
-
-    def handle_dataframe_func(self, input_table):
-        pass
-
     def __init__(
         self,
         sql,