freeradius3: Fix proxy.conf file conflict.

It was provided by both the freeradius3 and freeradius3-mod-realm packages.
Now provided by the freeradius3 package only.

Signed-off-by: Robby K <robbyke@gmail.com>

net/freeradius3/Makefile

@@ -345,7 +345,6 @@ define Package/freeradius3-mod-realm
 endef
 
 define Package/freeradius3-mod-realm/conffiles
-/etc/freeradius3/proxy.conf
 /etc/freeradius3/mods-available/realm
 /etc/freeradius3/mods-enabled/realm
 endef