Update for the KDB framework:
o Rename WITNESS_DDB to WITNESS_KDB. In the new world order KDB is the
acronym to use for debugging related code. The DDB option is used to enable the DDB debugger backend only.
o Likewise, rename DDB_TRACE to KDB_TRACE, rename DDB_UNATTENDED to
KDB_UNATTENDED and rename SC_HISTORY_DDBKEY to SC_HISTORY_KDBKEY.
o Remove DDB_NOKLDSYM. The new DDB backend supports pre-linker symbol
lookups as well as KLD symbol lookups at the same time.
o Remove GDB_REMOTE_CHAT. The GDB protocol hacks to allow this are
FreeBSD specific. At the same time, the GDB protocol has packets for console output.