Removed the conditional include from ruby_cups.h for ruby.h/st.h

This will raise a warning on pre Mavericks version of Mac OSX,
but will still compile successfully back to Ruby 1.8.7 on Mac OSX Lion
for sure.

This fixes compatibility with Mavericks.

ext/ruby_cups.h

@@ -1,13 +1,8 @@
 #include <cups/cups.h>
 
 // st.h is needed for ST_CONTINUE constant
-#ifdef __APPLE__
- #include <ruby.h>
- #include <st.h>
-#else
- #include <ruby.h>
- #include <st.h>
-#endif
+#include <ruby.h>
+#include <st.h>
 
 #ifndef MAXOPTS
  #define MAXOPTS 100