Fix applied gravity on soft bodies

Regression fix, gravity was accumulated between frames after some
changes around area gravity calculation.

Also got rid of unused member and method in soft body class.

servers/physics_3d/godot_soft_body_3d.cpp

@@ -964,12 +964,6 @@ void GodotSoftBody3D::apply_forces(const LocalVector<GodotArea3D *> &p_wind_area
 	}
 }
 
-void GodotSoftBody3D::_compute_area_gravity(const GodotArea3D *p_area) {
-	Vector3 area_gravity;
-	p_area->compute_gravity(get_transform().get_origin(), area_gravity);
-	gravity += area_gravity;
-}
-
 Vector3 GodotSoftBody3D::_compute_area_windforce(const GodotArea3D *p_area, const Face *p_face) {
 	real_t wfm = p_area->get_wind_force_magnitude();
 	real_t waf = p_area->get_wind_attenuation_factor();
@@ -987,12 +981,12 @@ void GodotSoftBody3D::predict_motion(real_t p_delta) {
 
 	ERR_FAIL_COND(!get_space());
 
-	int ac = areas.size();
-
 	bool gravity_done = false;
+	Vector3 gravity;
 
 	LocalVector<GodotArea3D *> wind_areas;
 
+	int ac = areas.size();
 	if (ac) {
 		areas.sort();
 		const AreaCMP *aa = &areas[0];

servers/physics_3d/godot_soft_body_3d.h

@@ -101,8 +101,6 @@ class GodotSoftBody3D : public GodotCollisionObject3D {
 	real_t drag_coefficient = 0.0; // [0,1]
 	LocalVector<int> pinned_vertices;
 
-	Vector3 gravity;
-
 	SelfList<GodotSoftBody3D> active_list;
 
 	Set<GodotConstraint3D *> constraints;
@@ -113,7 +111,6 @@ class GodotSoftBody3D : public GodotCollisionObject3D {
 
 	uint64_t island_step = 0;
 
-	_FORCE_INLINE_ void _compute_area_gravity(const GodotArea3D *p_area);
 	_FORCE_INLINE_ Vector3 _compute_area_windforce(const GodotArea3D *p_area, const Face *p_face);
 
 public: