Revert "report error when virProcessGetStatInfo() is unable to parse data"

Revert "report error when virProcessGetStatInfo() is unable to parse data"

This reverts commit 938382b60ae5bd1f83b5cb09e1ce68b9a88f679a.

Turns out, the commit did more harm than good. It changed
semantics on some public APIs. For instance, while
qemuDomainGetInfo() previously did not returned an error it does
now. While the calls to virProcessGetStatInfo() is guarded with
virDomainObjIsActive() it doesn't necessarily mean that QEMU's
PID is still alive. QEMU might be gone but we just haven't
realized it (e.g. because the eof handler thread is waiting for a
job).

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2041610
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>