Unify browser wrapper and utils

[jonathanKingston]

Reviewer:

Description:

This comes out of feedback @kdzwinel made for https://github.com/duckduckgo/duckduckgo-privacy-extension/pull/843 where it's not clear why wrapper and utils exist so I've unified them.

I also took the liberty to move to drop the .es6.js and use an import instead.

Steps to test this PR:

Automated tests:

• [ ] Unit tests
• [ ] Integration tests

Reviewer Checklist:

• [ ] Ensure the PR solves the problem
• [ ] Review every line of code
• [ ] Ensure the PR does no harm by testing the changes thoroughly
• [ ] Get help if you're uncomfortable with any of the above!
• [ ] Determine if there are any quick wins that improve the implementation

PR Author Checklist:

• [ ] Get advice or leverage existing code
• [ ] Agree on technical approach with reviewer (if the changes are nuanced)
• [ ] Ensure that there is a testing strategy (and documented non-automated tests)
• [ ] Ensure there is a documented monitoring strategy (if necessary)
• [ ] Consider systems implications