refactor(db_api): remove unused variables and add docs (#229)

* refactor: remove unused variables and add docs * refactor: nit

Author: HemangChothani

google/cloud/spanner_dbapi/connection.py

@@ -290,6 +290,10 @@ def run_statement(self, statement, retried=False):
  :type statement: :class:`dict`
  :param statement: SQL statement to execute.
 
+ :type retried: bool
+ :param retried: (Optional) Retry the SQL statement if statement
+ execution failed. Defaults to false.
+
  :rtype: :class:`google.cloud.spanner_v1.streamed.StreamedResultSet`,
  :class:`google.cloud.spanner_dbapi.checksum.ResultsChecksum`
  :returns: Streamed result set of the statement and a

google/cloud/spanner_dbapi/cursor.py

@@ -138,17 +138,10 @@ def callproc(self, procname, args=None):
  self._raise_if_closed()
 
  def close(self):
- """Prepare and execute a Spanner database operation.
-
- :type sql: str
- :param sql: A SQL query statement.
-
- :type args: list
- :param args: Additional parameters to supplement the SQL query.
- """
+ """Closes this cursor."""
  self._is_closed = True
 
- def _do_execute_update(self, transaction, sql, params, param_types=None):
+ def _do_execute_update(self, transaction, sql, params):
  sql = parse_utils.ensure_where_clause(sql)
  sql, params = parse_utils.sql_pyformat_args_to_spanner(sql, params)