release-21.2: util/mon: remove nameWithPointer to reduce allocations

[blathers-crl]

Backport 1/1 commits from #86954 on behalf of @yuzefovich.

/cc @cockroachdb/release

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This field was added in order to help us track down some of the memory
leaks which we have already found, and the field didn't turn out to be
that useful. When it was introduced, the implications on the increase in
allocations were unknown, and now I don't think the field is worth it.

name                                           old time/op    new time/op    delta
FlowSetup/vectorize=true/distribute=true-24       168µs ± 5%     164µs ± 4%  -2.33%  (p=0.007 n=19+20)
FlowSetup/vectorize=true/distribute=false-24      167µs ± 6%     164µs ± 6%    ~     (p=0.060 n=20+20)
FlowSetup/vectorize=false/distribute=true-24      163µs ± 4%     161µs ± 7%    ~     (p=0.057 n=19+20)
FlowSetup/vectorize=false/distribute=false-24     161µs ± 6%     159µs ± 5%    ~     (p=0.309 n=19+20)

name                                           old alloc/op   new alloc/op   delta
FlowSetup/vectorize=true/distribute=true-24      19.6kB ± 8%    19.0kB ± 8%  -2.62%  (p=0.001 n=19+18)
FlowSetup/vectorize=true/distribute=false-24     18.2kB ± 1%    17.7kB ± 1%  -2.56%  (p=0.000 n=17+16)
FlowSetup/vectorize=false/distribute=true-24     25.8kB ± 2%    25.4kB ± 0%  -1.44%  (p=0.000 n=16+16)
FlowSetup/vectorize=false/distribute=false-24    24.7kB ± 0%    24.4kB ± 1%  -1.36%  (p=0.000 n=16+16)

name                                           old allocs/op  new allocs/op  delta
FlowSetup/vectorize=true/distribute=true-24         218 ± 2%       205 ± 3%  -5.64%  (p=0.000 n=19+19)
FlowSetup/vectorize=true/distribute=false-24        208 ± 1%       197 ± 3%  -5.63%  (p=0.000 n=19+19)
FlowSetup/vectorize=false/distribute=true-24        206 ± 0%       197 ± 0%  -4.40%  (p=0.000 n=16+16)
FlowSetup/vectorize=false/distribute=false-24       197 ± 0%       188 ± 0%  -4.54%  (p=0.000 n=16+16)

Release justification: low-risk cleanup.

Release note: None

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[yuzefovich]

Friendly ping @michae2.

[michae2]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @yuzefovich)