qemu: fix build error with older platforms

qemu: fix build error with older platforms

Jim Fehlig reported on IRC that older gcc/glibc triggers this warning:

cc1: warnings being treated as errors
qemu/qemu_domain.c: In function 'qemuDomainDefFormatBuf':
qemu/qemu_domain.c:1297: error: declaration of 'remove' shadows a global declaration [-Wshadow]
/usr/include/stdio.h:157: error: shadowed declaration is here [-Wshadow]
make[3]: *** [libvirt_driver_qemu_impl_la-qemu_domain.lo] Error 1

Fix it like we have done in the past (such as commit 2e6322a).

* src/qemu/qemu_domain.c (qemuDomainDefFormatBuf): Avoid shadowing
a function name.

Signed-off-by: Eric Blake <eblake@redhat.com>