remove transaction from imdb import

Removing the transaction will allow other (async) operations to succeed
while the import is running, otherwise the database will be locked.
It also actually speeds up the import process, and there's no good
reason to roll back if the import aborts mid run.

unwind/imdb_import.py

@@ -189,8 +189,6 @@ async def import_from_file(*, basics_path: Path, ratings_path: Path):
     perc = 0.0
     perc_step = 0.001
 
-    async with db.shared_connection().transaction():
-
     chunk = []
 
     for i, m in enumerate(read_basics(basics_path)):