Revert "boot.js: Cross-frame version of st.assert"
Revert "boot.js: Cross-frame version of st.assert"

This reverts commit 75626551e5257fd2d7e445312af186f7b9e8116b.

adrian-castravete/amber,amber-smalltalk/amber,amber-smalltalk/amber,adrian-castravete/amber,amber-smalltalk/amber,adrian-castravete/amber