qemucaps2xmltest: Don't leak @binary
    
    There's no need to keep @binary around.
    virQEMUCapsInitGuestFromBinary() duplicates the string anyway.
    
     1,002 bytes in 36 blocks are definitely lost in loss record 54 of 59
        at 0x483579F: malloc (vg_replace_malloc.c:299)
        by 0x796B1C7: vasprintf (vasprintf.c:73)
        by 0x4C3F2C6: virVasprintfInternal (virstring.c:740)
        by 0x4C3F3DC: virAsprintfInternal (virstring.c:761)
        by 0x13AFC9: testGetCaps (qemucaps2xmltest.c:105)
        by 0x13B200: testQemuCapsXML (qemucaps2xmltest.c:157)
        by 0x13B642: virTestRun (testutils.c:174)
        by 0x13B366: doCapsTest (qemucaps2xmltest.c:191)
        by 0x13FF2B: testQemuCapsIterate (testutilsqemu.c:941)
        by 0x13B427: mymain (qemucaps2xmltest.c:215)
        by 0x13D706: virTestMain (testutils.c:1096)
        by 0x13B489: main (qemucaps2xmltest.c:221)
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>