remove non-functional doxygen generated navigation header from AtC doc files

doc/src/USER/atc/man_add_molecule.html

doc/src/USER/atc/man_add_species.html

doc/src/USER/atc/man_atom_element_map.html

doc/src/USER/atc/man_atom_weight.html

doc/src/USER/atc/man_atomic_charge.html

doc/src/USER/atc/man_boundary.html

doc/src/USER/atc/man_boundary_dynamics.html

doc/src/USER/atc/man_boundary_faceset.html

doc/src/USER/atc/man_boundary_integral.html

doc/src/USER/atc/man_consistent_fe_initialization.html

doc/src/USER/atc/man_contour_integral.html

doc/src/USER/atc/man_control.html

doc/src/USER/atc/man_control_momentum.html

doc/src/USER/atc/man_control_thermal.html

...ER/atc/man_control_thermal_correction_max_iterations.html

doc/src/USER/atc/man_decomposition.html

doc/src/USER/atc/man_electron_integration.html

doc/src/USER/atc/man_equilibrium_start.html

doc/src/USER/atc/man_extrinsic_exchange.html

doc/src/USER/atc/man_fe_md_boundary.html