Remove warning about disk space needed for uploads to S3

I am running Nextcloud 27.1.0, using an S3 bucket for primary storage.

As follows is one of the messages given under Security & setup warnings:

This instance uses an S3 based object store as primary storage. The uploaded files are stored temporarily on the server and thus it is recommended to have 50 GB of free space available in the temp directory of PHP. Check the logs for full details about the path and the available space. To improve this please change the temporary directory in the php.ini or make more space available in that path.

I have monitored the size and contents of directories for temporary files, as well as the application data directory, and the overall system disk usage, during uploads of large files. I have found no evidence of uploaded files being stored as temporary files.

Similarly, #27034 suggests that the message is obsolete (even though #19414 remains open).

If the message is obsolete, please remove it.

Otherwise, please clarify the current behavior.

Start by reproducing the Security & setup warning with S3 configured as primary storage, then inspect the current upload and temporary-file behavior described in the issue and compare it with #27034 and #19414. Done means either removing the obsolete warning or documenting the current behavior clearly, with a regression check for the resulting setup-warning behavior.