Schema: delete rows and sequences in the SQLite file strategy #145

Split from #124, part of #102. Moved to 8.0 because it changes what the following tests see.

• SqliteFileBasedSchemaStrategy::deleteData() and resetSequences() are no-ops. With USE_PRE_INITIALIZED_SCHEMA the rows of the previous test stay in the database.

Review note on the first implementation (branch feat/8.0): deleting in sqlite_master order fails with "FOREIGN KEY constraint failed" when PRAGMA foreign_keys=ON and child rows exist. Disable or defer the foreign key checks while deleting, like the MySQL strategy does.