Removed the hard-coded priming line when

both single_extruder_multi_material and wipe_tower are enabled,
and the print prints with a single extruder only.

Newly the same situation will be handled through a conditional G-code
in the following format:

{if not has_wipe_tower}
; Do the priming
{endif}

xs/src/libslic3r/GCode.hpp

@@ -90,7 +90,6 @@ public:
         m_brim_done(false) {}
 
     std::string prime(GCode &gcodegen);
-    static std::string prime_single_color_print(const Print & /* print */, unsigned int initial_tool, GCode & /* gcodegen */);
     void next_layer() { ++ m_layer_idx; m_tool_change_idx = 0; }
     std::string tool_change(GCode &gcodegen, int extruder_id, bool finish_layer);
     std::string finalize(GCode &gcodegen);