CLEANUP: 51d: register the deinitialization function

deinit_51degrees() is not called anymore from haproxy.c, removing
2 #ifdefs and one include. The function was made static. The include
file still includes 51Degrees.h which is needed by global.h and 51d.c
so it was not touched beyond this last function removal.
diff --git a/src/51d.c b/src/51d.c
index 3e3133a..37ee90c 100644
--- a/src/51d.c
+++ b/src/51d.c
@@ -600,7 +600,7 @@
 	return 0;
 }
 
-void deinit_51degrees(void)
+static void deinit_51degrees(void)
 {
 	struct _51d_property_names *_51d_prop_name, *_51d_prop_nameb;
 
@@ -654,4 +654,5 @@
 	cfg_register_keywords(&_51dcfg_kws);
 	hap_register_build_opts("Built with 51Degrees support.", 0);
 	hap_register_post_check(init_51degrees);
+	hap_register_post_deinit(deinit_51degrees);
 }