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)
latest merge request
Name Stage Failure
failed
unit:clang:freebsd12:amd64 Unit
Runtime platform                                    arch=amd64 os=freebsd pid=15380 revision=5316d4ac version=14.6.0
untracked: found 1511 files

Uploading artifacts as "archive" to coordinator... ok
id=2496182 responseStatus=201 Created token=syxBKyVA
Uploading artifacts...
Runtime platform
arch=amd64 os=freebsd pid=15383 revision=5316d4ac version=14.6.0
junit.xml: found 1 matching files and directories

Uploading artifacts as "junit" to coordinator... ok
id=2496182 responseStatus=201 Created token=syxBKyVA
Cleaning up project directory and file based variables
ERROR: Job failed: exit status 1

failed
system:clang:asan System
Uploading artifacts for failed job
Uploading artifacts...
untracked: found 1535 files

Uploading artifacts as "archive" to coordinator... 201 Created
id=2496195 responseStatus=201 Created token=1b1_X4PF
Uploading artifacts...
junit.xml: found 1 matching files and directories

Uploading artifacts as "junit" to coordinator... 201 Created
id=2496195 responseStatus=201 Created token=1b1_X4PF
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1