revert "fix #4333: redirect API handler output to STDERR"

revert "fix #4333: redirect API handler output to STDERR"

Redirecting stdout is not a feasible approach, as that also affects
all run_commands and other command executions/forks done by the API
handler, and thus breaks parsing outputs of such command executions
in the API handlers.

We plan to add a `--result-fd` option instead, allowing users to pass
their own file, open FD or named pipe to the pvesh, so that they can
process the output in streaming or in full afterward afterwards.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>