remove defunct ln_use_jattr option

Removal of ln_use_jattr option

This option is still included in the reference namelist with associated option handling in nemogcm.F90 and a declaration in par_oce.F90, however, the changes within iom.F90, domzgr.F90 and mppini.F90 that were triggered by its selection were removed at version 4.2

Details of this option are still included in the Sub-domain functionality section of the miscellaneous chapter of the reference manual. A separate issue will be opened there to ensure its removal.

Code implementation

Complete the removal of the optional in nemogcm.F90 and par_oce.F90 and remove its entry in cfgs/SHARED/namelist_ref

Documentation updates

Remove section from latex/NEMO/subfiles/chap_misc.tex