AMR: Remove ParmParse opal_coupling ( 4 * pi * \epsilon ).

Not final version since still hard-coded. In future we will
use the "OPAL-way", i.e.

double coefE = 1.0 / (4 * pi * epsilon_0);
Track::block->slbunch->setCouplingConstant(coefE);

modified:   src/Solvers/amr/Accel.H
modified:   src/Solvers/amr/Accel.cpp
modified:   src/Solvers/amr/Accel_advance.cpp
modified:   src/Solvers/amr/Electrostatic.H
modified:   src/Solvers/amr/Electrostatic.cpp
modified:   src/Structure/FieldSolver.cpp