qemuMigrationUpdateJobStatus (called in a loop by migration
and save tasks) uses qemuDomainObjEnterMonitorWithDriver;
however, that function ended up starting a nested job without
releasing the driver.

Since no one else is making nested calls, we can inline the
internal functions to properly track driver_locked.

* src/qemu/qemu_domain.h (qemuDomainObjBeginNestedJob)
(qemuDomainObjBeginNestedJobWithDriver)
(qemuDomainObjEndNestedJob): Drop unused prototypes.
* src/qemu/qemu_domain.c (qemuDomainObjEnterMonitorInternal):
Reflect driver lock to nested job.
(qemuDomainObjBeginNestedJob)
(qemuDomainObjBeginNestedJobWithDriver)
(qemuDomainObjEndNestedJob): Drop unused functions.