Debug: Use zoning dropdown for debug zoning modes

Control visibility using misc_debug 2, instead of controlling
debug modes themselves using misc_debug

src/debug_settings.h

@@ -49,12 +49,11 @@ inline bool HasGrfOptimiserFlag(NewGRFOptimiserFlags flag)
 
 enum MiscDebugFlags {
 	MDF_OVERHEAT_BREAKDOWN_OPEN_WIN,
-	MDF_ZONING_RS_WATER_FLOOD_STATE,
-	MDF_ZONING_RS_TROPIC_ZONE,
-	MDF_ZONING_RS_ANIMATED_TILE,
+	MDF_ZONING_DEBUG_MODES,
+	MDF_UNUSED1,
+	MDF_UNUSED2,
 	MDF_NEWGRF_SG_SAVE_RAW,
 	MDF_SPECIAL_CMDS,
-	MDF_ZONING_RS_WATER_REGION,
 };
 extern uint32_t _misc_debug_flags;