Drop trailing semi-colon from G_DEFINE_ macro

It's unnecessary, and only adds visual noise; we have been fairly
inconsistent in the past, but the semi-colon-less version clearly
dominates in the code base.

https://bugzilla.gnome.org/show_bug.cgi?id=669355

tests/refcount/closures.c

@@ -47,7 +47,7 @@ typedef struct {
 #define MY_TEST_GET_CLASS(test)    (G_TYPE_INSTANCE_GET_CLASS ((test), G_TYPE_TEST, GTestClass))
 
 static GType my_test_get_type (void);
-G_DEFINE_TYPE (GTest, my_test, G_TYPE_OBJECT);
+G_DEFINE_TYPE (GTest, my_test, G_TYPE_OBJECT)
 
 /* --- variables --- */
 static volatile gboolean stopping = FALSE;