qemu: remove dead code

Warning detected by Coverity.  No need for the NULL check, and
removing it silences the warning without any semantic change.

* src/qemu/qemu_migration.c (qemuMigrationFinish): All entries to
endjob had non-NULL vm.

src/qemu/qemu_migration.c

@@ -2569,14 +2569,12 @@ qemuMigrationFinish(struct qemud_driver *driver,
         VIR_WARN("Unable to encode migration cookie");
 
 endjob:
-    if (vm) {
     if (qemuMigrationJobFinish(driver, vm) == 0) {
         vm = NULL;
     } else if (!vm->persistent && !virDomainObjIsActive(vm)) {
         virDomainRemoveInactive(&driver->domains, vm);
         vm = NULL;
     }
-    }
 
 cleanup:
     if (vm)