release-23.1.0: distsql: fix sql.mem.distsql.current metric

[blathers-crl]

Backport 3/3 commits from #99887 on behalf of @yuzefovich.

/cc @cockroachdb/release

---

sql: don't create unused monitor and account

As of 961e66f we no longer need to
create memory monitors and accounts for sub- and post-queries so this
commit removes them.

Release note: None

util/mon: remove redundant locking in NewMonitorInheritWithLimit

This locking is no longer needed as of 472e740.

Release note: None

distsql: fix sql.mem.distsql.current metric

This commit fixes double counting of remote DistSQL flows' memory usage
against sql.mem.distsql.current metric. This was the case since we
passed the metric to both the flow monitor (created for all flows,
both local and remote) and the distsql monitor (which tracks the
memory usage of all remote flows). This is now fixed by only passing the
metric in the former case.

Fixes: #91787.

Release note (bug fix): Previously, sql.mem.distsql.current metric
would double count the memory usage of remote DistSQL flows and this has
been fixed.

---

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?

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is