v2.2: Revert "Thread manager instantiation in the validator (#4603)" (backport of #5132)

[mergify]

This reverts commit e48672c.

Problem

It isn't clear if the thread manager is the way we want to go long term. We should get consensus amongst the team / testing / data that shows benefit (including worst case scenarios) before instantiating the object in production. At the present, we spin up 24 extra threads that are unused as far as I am aware.

Summary of Changes

This reverts the commit that create a ThreadManager in Validator; the code remains but unused by agave-validator

---

This is an automatic backport of pull request #5132 done by Mergify.

[mergify]

Cherry-pick of 30c95ff has failed:

On branch mergify/bp/v2.2/pr-5132
Your branch is up to date with 'origin/v2.2'.

You are currently cherry-picking commit 30c95ff6e.
  (fix conflicts and run "git cherry-pick --continue")
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Changes to be committed:
	modified:   Cargo.lock
	modified:   core/Cargo.toml
	modified:   core/src/validator.rs
	modified:   local-cluster/src/validator_configs.rs
	modified:   thread-manager/Cargo.toml
	modified:   thread-manager/examples/core_contention_basics.rs
	modified:   thread-manager/examples/core_contention_sweep.rs
	deleted:    thread-manager/src/config.rs
	deleted:    thread-manager/src/default_config.toml
	modified:   thread-manager/src/lib.rs
	modified:   thread-manager/src/native_thread_runtime.rs
	modified:   thread-manager/src/rayon_runtime.rs
	modified:   thread-manager/src/tokio_runtime.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   programs/sbf/Cargo.lock
	both modified:   svm/examples/Cargo.lock

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