Remove very out of date load test scripts

[masih]

The scripts are untouched for about 4 years, hardcoding path to loadtest binary.

Remove them as they are redundant.

[cursor]

PR Summary

Low Risk
Documentation/tooling-only deletions with no runtime or CI references found in the codebase.

Overview
Removes three legacy helper scripts that have not been maintained for years and rely on hardcoded paths (e.g. /home/ubuntu/sei-chain/build/loadtest).

Deleted: run_constant_load.sh, run_loadtest.sh (load-test loop + metrics), and runtests.py (parallel go test / runtest.sh runner). Nothing in the repo references these files anymore.

^{Reviewed by Cursor Bugbot for commit db121f5. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Jun 15, 2026, 8:23 AM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.35%. Comparing base (0a2c388) to head (db121f5).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3585      +/-   ##
==========================================
- Coverage   59.22%   58.35%   -0.87%     
==========================================
  Files        2214     2140      -74     
  Lines      183389   174842    -8547     
==========================================
- Hits       108604   102031    -6573     
+ Misses      64994    63720    -1274     
+ Partials     9791     9091     -700     

Flag	Coverage Δ
sei-db	70.41% <ø> (ø)
sei-db-state-db	?

Flags with carried forward coverage won't be shown. Click here to find out more.
see 74 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.