Ignore partial data when removing files

On external storages, removing files sometimes tries to remove partial
data, represented in an array.

`lib/private/Files/Cache/Cache.php:remove()` doesn't support to process
arrays.

According to @icewind1991, we can ignore this partial data in
`remove()`.

Fixes: #26544
Signed-off-by: Jonas Meurer <jonas@freesources.org>