remove daemon/probes.h from .gitignore

The file daemon/probes.h used to be generated as part of a build, but
is no longer used. However, a stale copy of it lying around could
cause a build to fail. Removing it from .gitignore will make it more
likely someone will notice that they have it lying around.

.gitignore

@@ -54,7 +54,6 @@
 /daemon/libvirtd.8
 /daemon/libvirtd.8.in
 /daemon/libvirtd.pod
-/daemon/probes.h
 /docs/devhelp/libvirt.devhelp
 /docs/hvsupport.html.in
 /docs/libvirt-api.xml