Remove unused middleware helpers

[Ewgna]

Closes Issue 1921

Summary

Removed unused middleware helper functions and exports from the shared middleware module.

Important Changes

src/middleware/middleware.js

• Removed unused isCveProgramOrgMembershipObject placeholder function.
• Removed unused toLowerCaseArray helper.
• Removed unused rejectUnexpectedKeys helper.
• Removed the corresponding unused exports.

Testing

• 1) Ran node node_modules/eslint/bin/eslint.js src/middleware/middleware.js.
• 2) Ran node node_modules/mocha/bin/mocha test/unit-tests/middleware --recursive --exit.

Notes

• This PR only removes unused code; no runtime behavior is expected to change.