Do not use libxml2 deprecated functions
BIND can't be built when using libxml2 v2.10.0+ because of the warning messages.
The usage of xmlInitThreads() and xmlCleanupThreads() functions in libxml2 is now marked as deprecated, and these functions will be made private in the future.
Use xmlInitParser() and xmlCleanupParser() instead of them.
Closes #3518 (closed)