chore: drop web streams polyfilling on `globalThis` (#57077)
### What?
`globalThis.ReadableStream` and `globalThis.WriteableStream` has been exposed since Node.js 18, which is our new default requirement. (#56943)
### Why?
This simplifies the code and might result in slightly better performance.
### How?
Drop any checks of `globalThis` properties that are always defined now.
