Remove Contrast Menu for U8GLIB_ST7920

The other two devices we use in u8glib have more than only dummy code.
Checked this in the library code.

Marlin/Conditionals.h

@@ -130,7 +130,6 @@
      #define NEWPANEL
   #endif
 
-
   #ifdef ULTIPANEL
     #define NEWPANEL  //enable this if you have a click-encoder panel
     #define SDSUPPORT
@@ -161,6 +160,13 @@
     #define DEFAULT_LCD_CONTRAST 32
   #endif
 
+  #ifdef DOGLCD
+    #define HAS_LCD_CONTRAST
+    #ifdef U8GLIB_ST7920
+      #undefine HAS_LCD_CONTRAST
+    #endif
+  #endif
+
 #else // CONFIGURATION_LCD
 
   #define CONDITIONALS_H