devel/icu: Update distfile checksum and remove obsolete mirror

Upstream rerolled source package [1], [2], [3] and SourceForge no longer hosts recent versions.

1: https://gitlab.archlinux.org/archlinux/packaging/packages/icu/-/issues/1
2: https://git.alpinelinux.org/aports/commit/main/icu?id=fc95c59998285564fbcb0bfb2443898c62e10171
3: https://gitweb.gentoo.org/repo/gentoo.git/commit/dev-libs/icu?id=9df4e9b6496840e4614f26f1d6e0ce594084c0d7

PR: 277910
Reviewed by: jbeich
Approved by: portmgr (blanket)
MFH: 2024Q1