use SchemaEditor.execute() to run deferred_sql in migration sync_apps

[Lex Berezhny]

Associated GitHub Pull Request: ​https://github.com/django/django/pull/7579

This is a very simple fix for the sync_app method in the migration command that uses editor.execute() to execute deferred sql instead of directly using cursor.execute().

There are two reasons for this:

1. This is consistent with the normal migrateable apps workflow where deferred SQL is executed using editor.execute(). See: [django/db/backends/base/schema.py#L91](​https://github.com/django/django/blob/371adc472a2a1f09923101e3c4fda60cdff96028/django/db/backends/base/schema.py#L91)

2. When cursor.execute() is hard coded in sync_app it is not possible to do custom processing of the SQL (as could be done with a custom DatabaseSchemaEditor.execute()).

This pull request does not change any existing functionality and is backwards compatible but it provides a more consistent, intuitive and predictable behavior when extending DatabaseSchemaEditor.

[Tim Graham <timograham@…>]

In 8eb56f3c:

Fixed #27507 -- Used SchemaEditor.execute() to run deferred_sql in migrate's sync_apps().