fix(wasm): remove hardcoded isolation level

[flrgh]

Summary

This was added during local development to work around a bug but is no longer desired and disallows setting the isolation level via kong.conf.

Checklist

• The Pull Request has tests - not sure how to test 🤔...
• There's an entry in the CHANGELOG
• There is a user-facing docs PR

KAG-2347

[flrgh]

Let's wait until #11387 is merged, at which point I'll add a changelog entry and update kong.conf.default to reflect the fact that proxy_wasm_isolation is supported.

edit: done and unblocked

[team-gateway-bot]

The backport to release/3.4.x 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-release/3.4.x release/3.4.x
# Navigate to the new working tree
cd .worktrees/backport-release/3.4.x
# Create a new branch
git switch --create backport-11407-to-release/3.4.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 dbacabb627edc50d69a05a773cfe6f304667991f
# Push it to GitHub
git push --set-upstream origin backport-11407-to-release/3.4.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-release/3.4.x

Then, create a pull request where the base branch is release/3.4.x and the compare/head branch is backport-11407-to-release/3.4.x.