Do not force commit in computed fields

The following commit leads to `CacheMissed` errors when retrieving an
album image for the first time:
odoo/odoo@0f6875a

It happens because a call to `commit` also clears the cache.

In order to fix the issue, we could assign the value to the computed
field after the `commit` call. However, the programmatic call to
`commit` is not necessary since it happens automatically at the end of
the transaction.

models/oomusic_folder.py

@@ -291,7 +291,6 @@ def _compute_image_big(self):
             # Save in cache
             try:
                 folder.sudo().write({"image_big_cache": resized_image})
-                self.env.cr.commit()
             except OperationalError:
                 _logger.warning(
                     "Error when writing image cache for folder id: %s", folder.id, exc_info=True
@@ -324,7 +323,6 @@ def _compute_image_medium(self):
             # Save in cache
             try:
                 folder.sudo().write({"image_medium_cache": resized_image})
-                self.env.cr.commit()
             except OperationalError:
                 _logger.warning(
                     "Error when writing image cache for folder id: %s", folder.id, exc_info=True
@@ -357,7 +355,6 @@ def _compute_image_small(self):
             # Save in cache
             try:
                 folder.sudo().write({"image_small_cache": resized_image})
-                self.env.cr.commit()
             except OperationalError:
                 _logger.warning(
                     "Error when writing image cache for folder id: %s", folder.id, exc_info=True