coverity-model: make g_free a synonym of free

coverity-model: make g_free a synonym of free

Recently, Coverity has started complaining about using g_free() to free
memory areas allocated by GLib functions not included in model.c,
such as g_strfreev.  This unfortunately goes against the GLib
documentation, which suggests that g_malloc() should be matched
with g_free() and plain malloc() with free(); since GLib 2.46 however
g_malloc() is hardcoded to always use the system malloc implementation,
and g_free is just "free" plus a tracepoint.  Therefore, this
should not cause any problem in practice.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>