www/nghttp2: Update to 1.51.0
* Switch to CMake (simplifies patching a lot)
* Drop ASIO option (removed in 1.52.0)
* Remove ancient version dependencies of libraries to simplify port
* Make use of helpers instead of patching by hand
* Modernize Makefile to follow Porters Handbook more closely
Reference: https://github.com/nghttp2/nghttp2/pull/1844
Changelog: https://github.com/nghttp2/nghttp2/releases/tag/v1.51.0
PR: 268537
Approved by: portmgr (maintainer timeout, 2+ weeks)