Fix: libcrmcommon: Drop deprecated libxml2 symbols

xmlLoadExtDtdDefaultValue should be replaced by the XML_PARSE_DTDLOAD
parser option. However, we don't call any function that accepts parser
options where we currently use xmlLoadExtDtdDefaultValue. We also don't
use an xmlParserCtxt, so we can't call xmlCtxtUseOptions(). (There's no
analog for xmlRelaxNGParserCtxt.)

xmlSubstituteEntitiesDefault() should be replaced by XML_PARSE_NOENT.
Similarly, we don't call any function that accepts parser options where
we currently use xmlSubstituteEntitiesDefault().

xmlLineNumbersDefault() is always enabled by the modern parser API.

xmlParseFile() should be replaced by xmlReadFile(). Here we use a NULL
encoding and no options.

Note that the "new" or "modern" libxml2 parser API was released over 20
years ago, and we already use it in other places. So backwards
compatibility should not be a concern.

No regression tests change.

Ref T719
Ref CLBZ#5530

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>