Work around Doxygen 1.9.7 change

Work around Doxygen 1.9.7 change

Doxygen 1.9.7 avoids duplicating member definitions in the XML
documents for groups and header files (doxygen/doxygen#9797).  This
change breaks the current Doxygen-REST bridge, which expects to find
memberdef elements in krb5_8hin.xml.  To work around this problem,
remove the @group and @ref declarations in krb5.hin; they were not
translated into REST as it was.

Also remove a deprecated setting in Doxyfile.

ticket: 9104 (new)
tags: pullup
target_version: 1.21-next
target_version: 1.20-next