These features were for Celery 4.2.1, since this version
has a regression, version 4.1.1 is used instead.
The version 4.2.1 features are removed also and implemented
in code.
Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>
Add retry to race condition in intermediate image generation.
Remove DB index from cache file size field.
Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>