chore(builder): remove flashblocks extra context

[danyalprout]

Remove the extra context for Flashblocks, this can just be included by default. See https://github.com/base/node-reth/pull/421/changes#diff-80a0fc8a86560eb4091387fa7ff729acf7cc116881c3dde98ae70ee329482ab6R54

[Farukest]

Hi @danyalprout, I'm eliminating the issues one by one with your permission. Hope it's okay :)