Remove `@export` from functions which don't need to be public

[nicholascarey]

When you do this add @keywords internal to the roxygen tags, which will mean the function and help documentation will not appear in the index (though i think you need to delete the man folder and run roxygen again to rebuild the documentation or it does not get removed).

[nicholascarey]

Smaller utility functions could also go in the utils.R file which will help keep the folder tidier. They can also go in other .R files - e.g. if an internal function is used in only one exported function it's common to just put it at the bottom of the exported function script.

Can also group related functions in a single file like I have done with utils.R. Basically as long as they are in the R folder somewhere they will work fine.

[rix133]

I think most obsolete functions are now removed but should any of those also be removed from exports (not used in vignettes currently):

• [ ] applyGenerateProbs
• [ ] createTableOfRDBESIds
• [ ] estim
• [ ] filterAndTidyRDBESDataObject
• [ ] fixSLids
• [ ] generateMissingSSRows
• [ ] generateNAsUsingSL
• [ ] generateProbs
• [ ] generateZerosUsingSL
• [ ] getTablesInRDBESHierarchy
• [ ] newRDBESDataObject
• [ ] removePrefixFromVarNames
• [ ] runChecksOnSelectionAndProbs

I think if a function is not used in a vignette it should not be exported but the vignettes are currently incomplete #163

[rix133]

we can keep it as is