icu: remove icu4c-54.1

Only zoom-us depends on icu4c-54.1. Since we know that version has some vulnerabilities, and zoom-us appears to work with icu4c-57.1, I remove the icu/54.1.nix file, remove icu_54_1 from all-packages.nix, and have zoom-us depend on icu (i.e., icu4c-57.1)