Update to 1.28.1

Hi @markus,

I took the freedom to update asio to 1.28.1 while applying also !1.

Since there is now a pkgconfig file, I had to change the package to arch any. I also had to remove some build files that were created for the examples.

On my fork (https://salsa.debian.org/stephanlachnit/libasio), you can also find the upstream and pristine-tar branches, as well as the upstream/1.28.1 and debian/1.28.1-0.1 tags.

I will upload this as NMU with 10 days as delay, since my goal is to have asio 1.28 in Ubuntu 24.04, for which the import freeze is on the 29th of February.