roachtest: Delete scbench randomload test

[rimadeodhar]

This test has been skipped for a year and based
on the history of the test hasn't been providing
much value. We can delete it now. Random
schema change testing is covered by schemachange/randomload.

Epic: none
Fixes: #56230
Release note: None

[cockroach-teamcity]

This change is 

[rimadeodhar]

TFTR!

bors r=rafiss

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from 63c1553 to blathers/backport-release-22.2-105919: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.2.x failed. See errors above.

---

error creating merge commit from 63c1553 to blathers/backport-release-23.1-105919: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 23.1.x failed. See errors above.

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