Hard deprecate the metacore argument

[vedhav]

Changes Description

The use of metacore argument will now throw an error instead of a warning message.

Task List

• The spirit of xportr is met in your Pull Request
• Place Closes Move from Deprecate Warn to Deprecate Error #203 into the beginning of your Pull Request Title (Use Edit button in top-right if you need to update)
• Summary of changes filled out in the above Changes Description. Can be removed or left blank if changes are minor/self-explanatory.
• Code is formatted according to the tidyverse style guide. Use styler package and functions to style files accordingly.
• Updated relevant unit tests or have written new unit tests. See our Wiki for conventions used in this package.
• Creation/updated relevant roxygen headers and examples. See our Wiki for conventions used in this package.
• Run devtools::document() so all .Rd files in the man folder and the NAMESPACE file in the project root are updated appropriately
• Run pkgdown::build_site() and check that all affected examples are displayed correctly and that all new/updated functions occur on the "Reference" page.
• Update NEWS.md if the changes pertain to a user-facing function (i.e. it has an @export tag) or documentation aimed at users (rather than developers)
• Make sure that the pacakge version in the NEWS.md and DESCRIPTION file is same. Don't worry about updating the version because it will be auto-updated using the vbump.yaml CI.
• Address any updates needed for vignettes and/or templates
• Link the issue Development Panel so that it closes after successful merging.
• Fix merge conflicts
• Pat yourself on the back for a job well done! Much love to your accomplishment!

[vedhav]

Before merging please make sure that the version would be auto-bumped to the one mentioned in the PR. Right now it's 0.3.1.9005