Remove unused variable mapclass::towercol

This variable is written to, but is never actually read. Writing to a
variable doesn't really do anything unless you read from it somewhere
else.

desktop_version/src/Map.h

@@ -114,7 +114,6 @@ public:
     //This is the old colour cycle
     int r, g,b;
     int check, cmode;
-    int towercol;
     int colstate, colstatedelay;
     int colsuperstate;
     int spikeleveltop, spikelevelbottom;