jemalloc does not play nice with our Rust library (proxmox-backup-qemu),
specifically it never releases memory allocated from Rust to the OS.
This leads to a problem with larger caches (e.g. for the PBS block driver).
It appears to be related to this GitHub issue:
https://github.com/jemalloc/jemalloc/issues/1398
The background_thread solution seems weirdly hacky, so let's disable
jemalloc entirely for now.
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>