Drop support for IconSymbolizer.size

[KaiVolland]

Description

This drops the support for size in the IconSymbolizer as it was handled very inconvenient which led to confusion:

https://github.com/geostyler/geostyler/issues/1746 https://github.com/geostyler/geostyler-openlayers-parser/issues/624

The upcoming ol release will include width and height for the ol/style/Icon so we will be able to implement it correctly with the next ol version:

https://github.com/openlayers/openlayers/pull/14364

Pull request type

Please check the type of change your PR introduces:

• [x] Bugfix
• [ ] Feature
• [ ] Dependency updates
• [x] Code style update (formatting, renaming)
• [ ] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] Documentation content changes
• [ ] Other (please describe)
• [ ] I am unsure (we'll look into it together)

Do you introduce a breaking change?

• [x] Yes
• [ ] No
• [ ] I am unsure (no worries, we'll find out)

Checklist

• [x] I understand and agree that the changes in this PR will be licensed under the BSD 2-Clause License
• [x] I have followed the guidelines for contributing
• [x] The proposed change fits to the content of the code of conduct
• [x] I have added or updated tests and documentation, and the test suite passes (run npm test locally)
• [ ] I'm lost; why do I have to check so many boxes? Please help!