Disable 16bpp drawing code since nothing of it is currently used anyway

src/r_draw.c

@@ -801,4 +801,6 @@ void R_DrawViewBorder(void)
 //                   INCLUDE 16bpp DRAWING CODE HERE
 // ==========================================================================
 
+#ifdef HIGHCOLOR
 #include "r_draw16.c"
+#endif

src/r_draw.h

@@ -169,11 +169,13 @@ void R_DrawColumnShadowed_8(void);
 // 16bpp DRAWING CODE
 // ------------------
 
+#ifdef HIGHCOLOR
 void R_DrawColumn_16(void);
 void R_DrawWallColumn_16(void);
 void R_DrawTranslucentColumn_16(void);
 void R_DrawTranslatedColumn_16(void);
 void R_DrawSpan_16(void);
+#endif
 
 // =========================================================================
 #endif  // __R_DRAW__