make compile_snippet use Eigen/Dense

doc/snippets/compile_snippet.cpp.in

diff --git a/doc/snippets/compile_snippet.cpp.in b/doc/snippets/compile_snippet.cpp.in
index 4745423..894cd52 100644
--- a/doc/snippets/compile_snippet.cpp.in
+++ b/doc/snippets/compile_snippet.cpp.in
@@ -1,10 +1,4 @@
-#include <Eigen/Core>
-#include <Eigen/LU>
-#include <Eigen/QR>
-#include <Eigen/Cholesky>
-#include <Eigen/Geometry>
-#include <Eigen/Jacobi>
-#include <Eigen/Eigenvalues>
+#include <Eigen/Dense>
 #include <iostream>
 
 using namespace Eigen;