Remove vectors feature check in 7.15+

[stevejgordon]

This is removed in 7.15.0 - See elastic/elasticsearch#76068

[github-actions]

The backport to master failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-master master
# Navigate to the new working tree
cd .worktrees/backport-master
# Create a new branch
git switch --create backport-5993-to-master
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 fc1ed40d16cb986b2994c1c93f969e507068b8bf
# Push it to GitHub
git push --set-upstream origin backport-5993-to-master
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-master

Then, create a pull request where the base branch is master and the compare/head branch is backport-5993-to-master.