domain_event: Resolve memory leak found by Valgrind
domain_event: Resolve memory leak found by Valgrind

Commit id '4421e257' strdup'd devAlias, but didn't free

Running qemuhotplugtest under valgrind resulted in the following:

==7375== 9 bytes in 1 blocks are definitely lost in loss record 11 of 70
==7375==    at 0x4A0887C: malloc (vg_replace_malloc.c:270)
==7375==    by 0x37C1085D71: strdup (strdup.c:42)
==7375==    by 0x4CBBD5F: virStrdup (virstring.c:554)
==7375==    by 0x4CFF9CB: virDomainEventDeviceRemovedNew (domain_event.c:1174)
==7375==    by 0x427791: qemuDomainRemoveChrDevice (qemu_hotplug.c:2508)
==7375==    by 0x42C65D: qemuDomainDetachChrDevice (qemu_hotplug.c:3357)
==7375==    by 0x41C94F: testQemuHotplug (qemuhotplugtest.c:115)
==7375==    by 0x41D817: virtTestRun (testutils.c:168)
==7375==    by 0x41C400: mymain (qemuhotplugtest.c:322)
==7375==    by 0x41DF3A: virtTestMain (testutils.c:764)
==7375==    by 0x37C1021A04: (below main) (libc-start.c:225)

olafhering/libvirt,libvirt/libvirt,fabianfreyer/libvirt,agx/libvirt,nertpinx/libvirt,andreabolognani/libvirt,taget/libvirt,elmarco/libvirt,nertpinx/libvirt,zippy2/libvirt,cbosdo/libvirt,jardasgit/libvirt,agx/libvirt,taget/libvirt,crobinso/libvirt,zhlcindy/libvirt-1.1.4-maintain,eskultety/libvirt,taget/libvirt,nertpinx/libvirt,crobinso/libvirt,fabianfreyer/libvirt,crobinso/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,zhlcindy/libvirt-1.1.4-maintain,fabianfreyer/libvirt,cbosdo/libvirt,eskultety/libvirt,agx/libvirt,libvirt/libvirt,andreabolognani/libvirt,rlaager/libvirt,jfehlig/libvirt,jardasgit/libvirt,datto/libvirt,libvirt/libvirt,rlaager/libvirt,zippy2/libvirt,andreabolognani/libvirt,olafhering/libvirt,zippy2/libvirt,VenkatDatta/libvirt,rlaager/libvirt,agx/libvirt,jardasgit/libvirt,datto/libvirt,shugaoye/libvirt,rlaager/libvirt,shugaoye/libvirt,agx/libvirt,cbosdo/libvirt,cbosdo/libvirt,shugaoye/libvirt,datto/libvirt,crobinso/libvirt,zhlcindy/libvirt-1.1.4-maintain,eskultety/libvirt,libvirt/libvirt,zhlcindy/libvirt-1.1.4-maintain,andreabolognani/libvirt,elmarco/libvirt,olafhering/libvirt,taget/libvirt,andreabolognani/libvirt,nertpinx/libvirt,jardasgit/libvirt,shugaoye/libvirt,datto/libvirt,VenkatDatta/libvirt,elmarco/libvirt,jfehlig/libvirt,eskultety/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,elmarco/libvirt,elmarco/libvirt,zhlcindy/libvirt-1.1.4-maintain,olafhering/libvirt,jardasgit/libvirt,eskultety/libvirt,cbosdo/libvirt,jfehlig/libvirt,jfehlig/libvirt,rlaager/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,taget/libvirt,zippy2/libvirt,shugaoye/libvirt,datto/libvirt