Removed m_coll_offsets and tidied up UpdateFactor method

Issue/feature addressed

Array of offsets for collections are no longer required in ExpList

Proposed solution

Remove m_coll_phys_offset and m_coll_coeffs_offset arrays in ExpList. It was also being used in UpdateFactor in Collections so have removed that argument from this function. Finally there were alot of unnecssary virtual instances of UpdateFactor so removed these and changed the function pure virtual to an ordinary virtual function

Implementation

As above

Tests

Suggested reviewers

Dave wanted this done so have put him down.

Checklist

• Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).