Remove external dependencies
Many distros ship libxml2 with zlib, liblzma and ICU support enabled, see for example https://packages.debian.org/sid/libxml2. These dependencies are largely unneeded and increase the attack surface of libxml2.
To remove ICU support, see #708.
Support for compression libraries has been disabled by default in f7f14537. It's impossible to know how many people rely on this feature. I'd expect that the new defaults will be picked up by less conservative distros which might lead to more insights. Over the next releases, I plan to
- also disable liblzma in the legacy build
- disable zlib in the legacy build
- eventually remove compression support
This only leaves libiconv as an external dependency on non-POSIX platforms.