Don't try delete old ingester blocks without bucket store configured

[bryanhuhta]

When running Pyroscope without bucket storage configured (this typically occurs when running locally in monolith mode), the ingester block cleaner tries to clean blocks off disk. However, since a shipper isn't running, no shipper.json file is created and the cleaner logs the following error:

ts=2024-01-29T12:54:11.499628801Z caller=retention.go:147 level=error msg="failed to delete uploaded blocks, could not get blocks for tenant" err="open data/anonymous/local/shipper.json: no such file or directory" tenantID=anonymous

We should account for shipper.json not existing by turning off the block cleaner. We should also log a warn level message (or no message at all) when this occurs instead of an error, since it's not exactly an error scenario.