Remove unimplemented static variant functions 'blend' and 'interpolat…

…e'. If a user attempts to call either of these it will introduce a linker error and it may not be immediately clear to them why. Also, variant interpolation can already be accessed via 'UtilityFunctions::lerp', making at least the interpolate function unecessary here.

include/godot_cpp/variant/variant.hpp

@@ -327,8 +327,6 @@ class Variant {
 	bool booleanize() const;
 	String stringify() const;
 	Variant duplicate(bool deep = false) const;
-	static void blend(const Variant &a, const Variant &b, float c, Variant &r_dst);
-	static void interpolate(const Variant &a, const Variant &b, float c, Variant &r_dst);
 
 	static String get_type_name(Variant::Type type);
 	static bool can_convert(Variant::Type from, Variant::Type to);