qemu: remove unnecessary virBufferFreeAndReset() after virCommandAddArgBuffer()
qemu: remove unnecessary virBufferFreeAndReset() after virCommandAddArgBuffer()

The latter function is guaranteed to always clear out the virBuffer
anyway, so this is redundant and could add to extra cargo-cult code if
used as an example.

Signed-off-by: Laine Stump <c23361c43fbf79fed83e8b76173707b083d6caf5@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

libvirt/libvirt,olafhering/libvirt,nertpinx/libvirt,olafhering/libvirt,crobinso/libvirt,crobinso/libvirt,jardasgit/libvirt,jfehlig/libvirt,nertpinx/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,jfehlig/libvirt,nertpinx/libvirt,jardasgit/libvirt,crobinso/libvirt,jardasgit/libvirt,zippy2/libvirt,jardasgit/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,olafhering/libvirt,nertpinx/libvirt,jardasgit/libvirt