Clean up fctx_minimize_qname

Remove 'fname', we only need the dns_name_t structure in it, so
convert 'name' from a pointer to a structure.  Remove redundant
variables 'dbuf' and 'nbuf', 'tmpname' structure has these.  Remove
redundant initialisation of 'tmpname'.  Formally handle concatenation
failure by ending qname mininisation.
65 jobs for !6265 with 3324-clean-up-fctx_minimize_qname in 18 minutes and 30 seconds (queued for 4 seconds)
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