Remove StorageStatistics from Files

[imsdu]

Motivation
New features (S3 multipart upload, registering directories) makes it difficult to control a priori that a file do not exceed the max capacity set for the storage (spoiler: it was already the case for ).

As StorageStatistics makes Files more complex and couples it to Elasticsearch, it should be removed

Acceptance criteria

1. StorageStatistics and the checks/tests/docs it introduces are removed

Not in scope

1. Implement a posteriori a way to control capacity for storages