delta[3] not used when DELTA not defined.

got:
Marlin_main.cpp:387: warning: 'delta' defined but not used

Compiles cleaner when definition is removed.

Marlin/Marlin_main.cpp

 const char axis_codes[NUM_AXIS] = {'X', 'Y', 'Z', 'E'};
 static float destination[NUM_AXIS] = { 0, 0, 0, 0 };
 
-#ifndef DELTA
-  static float delta[3] = { 0, 0, 0 };
-#endif
-
 static float offset[3] = { 0, 0, 0 };
 static bool home_all_axis = true;
 static float feedrate = 1500.0, next_feedrate, saved_feedrate;