pythongh-90923: Improve sqlite3.Connection.execute* docs (python#91643)

- Drop 'nonstandard'; it does not add any value
- Try to be more concise
- Make return value a little more explicit

Author: Erlend Egeberg Aasland

Doc/library/sqlite3.rst

@@ -431,24 +431,21 @@ Connection Objects
 
    .. method:: execute(sql[, parameters])
 
-      This is a nonstandard shortcut that creates a cursor object by calling
-      the :meth:`~Connection.cursor` method, calls the cursor's
-      :meth:`~Cursor.execute` method with the *parameters* given, and returns
-      the cursor.
+      Create a new :class:`Cursor` object and call
+      :meth:`~Cursor.execute` on it with the given *sql* and *parameters*.
+      Return the new cursor object.
 
    .. method:: executemany(sql[, parameters])
 
-      This is a nonstandard shortcut that creates a cursor object by
-      calling the :meth:`~Connection.cursor` method, calls the cursor's
-      :meth:`~Cursor.executemany` method with the *parameters* given, and
-      returns the cursor.
+      Create a new :class:`Cursor` object and call
+      :meth:`~Cursor.executemany` on it with the given *sql* and *parameters*.
+      Return the new cursor object.
 
    .. method:: executescript(sql_script)
 
-      This is a nonstandard shortcut that creates a cursor object by
-      calling the :meth:`~Connection.cursor` method, calls the cursor's
-      :meth:`~Cursor.executescript` method with the given *sql_script*, and
-      returns the cursor.
+      Create a new :class:`Cursor` object and call
+      :meth:`~Cursor.executescript` on it with the given *sql_script*.
+      Return the new cursor object.
 
    .. method:: create_function(name, num_params, func, *, deterministic=False)