Remove es5.js and browser check from html files

[jna4k]

Description

This PR removes the es5.js file that was being loaded from a external CDN. It also removes a browser check that redirected the user to the "unsupported browser page" if the user were using a browser other than chrome, firefox, edge or safari. The PR also removes said unspported browser page.

Please check if the PR fulfills these requirements

• The commit message follows our guidelines: https://github.com/geosolutions-it/MapStore2/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x", remove the others)

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

Issue

What is the current behavior?
We are currently using a 3rd party javascript file from a CDN, and uses it to check the users browser version, if the user is using Internet Explore they will be redirected to a unsupported browser page.

#12477

What is the new behavior?
We will no longer load the es5.js file and the we will no longer do the browser check. This means if the user is using a unspported browser, the site will simply fail.

Breaking change

Does this PR introduce a breaking change? (check one with "x", remove the other)

• Yes, and I documented them in migration notes
• No

Other useful information