Enable misc ex15 more often

I'm not sure when we got around to fixing the compatibilities here, but
they're working fine now.

Author: roystgnr

examples/miscellaneous/miscellaneous_ex15/miscellaneous_ex15.C

@@ -170,17 +170,6 @@ int main (int argc, char** argv)
   libmesh_example_requires(false, "--enable-ifem");
 #else
 
-#ifdef LIBMESH_ENABLE_NODE_CONSTRAINTS
-  // Node constraints are not yet implemented for infinite elements.
-  libmesh_example_requires(false, "--disable-node-constraints");
-#endif
-
-#ifdef LIBMESH_ENABLE_SECOND_DERIVATIVES
-  // UniformRefinement uses second derivatives if they are enabled,
-  // but for infinite elements they are not implemented.
-  libmesh_example_requires(false, "--disable-second");
-#endif
-
   // Skip this example if libMesh was compiled with <3 dimensions.
   // INFINITE ELEMENTS ARE IMPLEMENTED ONLY FOR 3 DIMENSIONS AT THE MOMENT.
   libmesh_example_requires(3 <= LIBMESH_DIM, "3D support");