Remove container specific import from __init__.py (#14)

Author: petkaze

testcontainers/__init__.py

@@ -1,6 +1,2 @@
-from testcontainers.selenium import BrowserWebDriverContainer
-from testcontainers.mysql import MySqlContainer
-from testcontainers.postgres import PostgresContainer
-from testcontainers.oracle import OracleDbContainer
 from testcontainers.core.generic import GenericContainer
 from testcontainers.core.waiting_utils import wait_container_is_ready, wait_for