Suppress FileNotFoundError when deleting non-existent keys in the obstore adapter.

When writing empty chunks (i.e. chunks where all values are equal to the array's fill value) to a zarr array, zarr will delete those chunks from the underlying store. For zarr arrays backed by the obstore adapter, this will potentially raise a FileNotFoundError if the chunk doesn't already exist. Since whether or not a delete of a non-existing object raises an error depends on the behavior of the underlying store, suppressing the error in all cases results in consistent behavior across stores, and is also what zarr seems to expect from the store.