main/icu: upgrade to 65.1

prepare() was removed because the issues have been fixed with:

• https://github.com/unicode-org/icu/commit/f2d8d1be68dfe12abe5237f0c14bb6da951e0d78
• https://github.com/unicode-org/icu/commit/c620f117ca4ad8eb1a3613d115fc3f4d3871ccb6
• https://github.com/unicode-org/icu/commit/be63df401e118aa45a574c27be2e65564c27739a