Create GC3 package branch for coupling branches

[frrh]

Context

The UKMO GC3 coupled model features a number of branches related to coupling which are not part of the core GO6/GSI8 configuration.

We need to review these and, where necessary, merge them into a single coupling package branch in order to

• bring these branches up to date for ease of management/maintenance
• dispense with redundant or unnecessary code
• minimise the number of NEMO branches employed in an official GC3 configuration
• reduce complexity to facilitate ease of future developments

The continued use of some branches is questionable.... e.g. one branch makes a single line change yet has been through at least two subsequent trunk upgrades making it impossible to merge into a suitable 3.6 based branch and which on close inspection now appears essentially redundant.

Analysis

Background details, investigations and procedures are recorded here: wiki:ticket/1737/General

Fix

Created brand new NEMO vn 3.6 versions of existing component branches:

​branches/UKMO/dev_r5518_hadgem3_cplfld
branches/UKMO/dev_r5518_hadgem3_cplseq
branches/UKMO/dev_r5518_hadgem3_mct (removing use of key_oasis3mct and replacing with the standard NEMO base code practise of using key_oasis3)
​branches/UKMO/dev_r5518_xios_initialize_toyoce

These were used to create package branch:

branches/UKMO/dev_r5518_GC3_couple_pkg

Use of this branch requires that any jobs previously employing key_oasis3mct should now use key_oasis3 instead.

It has been decided that henceforth, branches/UKMO/dev_r5518_GC3_couple_pkg will be used as the sole GC3 coupling-related branch. i.e. there is no longer any reason to keep the component branches as separate entities so we have deleted those and should any future developments become necessary they will be applied directly to branches/UKMO/dev_r5518_GC3_couple_pkg.

[frrh]

The package branch must be kept under constant review and brought up to date with any new or changes to existing component branches.