Remove unused code

[kaikalur]

We tried to get distinct+limit only queries to work via various different hacks until we finally figured out the right way in:

#17640

So removing this deadcode that was introduced in two PRs:

#17199
#17536

Test plan - tests exist

== RELEASE NOTES ==

General Changes
* Removed two unused session params - `hash_based_distinct_limit_enabled` and `hash_based_distinct_limit_threshold` and the corresponding implementation in favor of the `quick_distinct_limit_enabled` feature.

[jainxrohit]

Add release note for removing the existing config?

[jainxrohit]

can we add some description in commit on what is being removed?

[kaikalur]

can we add some description in commit on what is being removed?

done

[kaikalur]

Add release note for removing the existing config?

Hmm ok maybe. I don't think anyone uses these - these are very specific enable/disable "feature" flags.

[jainxrohit]

Add release note for removing the existing config?

Hmm ok maybe. I don't think anyone uses these - these are very specific enable/disable "feature" flags.

Since we dont visibility in to external usage, it may be safe to assume that they might be?

[kaikalur]

Add release note for removing the existing config?

Hmm ok maybe. I don't think anyone uses these - these are very specific enable/disable "feature" flags.

Since we dont visibility in to external usage, it may be safe to assume that they might be?

Done