Implement regularizations for Euler eq

Implements the Navier-Stokes and general regularization from J.-L. Guermond and B. Popov, “Viscous regularization of the euler equations and entropy principles,” SIAM Journal on Applied Mathematics, vol. 74, no. 2, pp. 284–305, 2014.

src/EulerEq/callbacks.jl

@@ -45,9 +45,9 @@ function callback_equation(state_u, state_t, env, P, isperiodic, eq::EulerEquati
   t       .= state_t
   Sm1     .= S
   flx_Sm1 .= flx_S
-  dg1d.new_broadcast_volume!(pressure, equation, env.mesh)
-  @unpack rho, q = get_dynamic_variables(cache)
-  @unpack p, eps = get_static_variables(cache)
+  # dg1d.new_broadcast_volume!(pressure, equation, env.mesh)
+  # @unpack rho, q = get_dynamic_variables(cache)
+  # @unpack p, eps = get_static_variables(cache)
   dg1d.new_broadcast_volume!(entropy_variables, equation, env.mesh)
 end