Math Lib: rotate matrix cleanup

- Remove 'rotate_m2', unlike 'rotate_m4' it created a new matrix
  duplicating 'angle_to_mat2' - now used instead.
  (better avoid matching functions having different behavior).

- Add 'axis_angle_to_mat4_single',
  convenience wrapper for 'axis_angle_to_mat3_single'.

- Replace 'unit_m4(), rotate_m4()' with a single call to 'axis_angle_to_mat4_single'.

source/blender/collada/collada_internal.cpp

@@ -33,11 +33,8 @@
 
 UnitConverter::UnitConverter() : unit(), up_axis(COLLADAFW::FileInfo::Z_UP)
 {
-	unit_m4(x_up_mat4);
-	rotate_m4(x_up_mat4, 'Y', -0.5 * M_PI);
-
-	unit_m4(y_up_mat4);
-	rotate_m4(y_up_mat4, 'X', 0.5 * M_PI);
+	axis_angle_to_mat4_single(x_up_mat4, 'Y', -0.5 * M_PI);
+	axis_angle_to_mat4_single(y_up_mat4, 'X', 0.5 * M_PI);
 
 	unit_m4(z_up_mat4);
 	unit_m4(scale_mat4);