I found a better solution to remove the three font buttons.
1) Rename /js/xenforo/bb_code_edit.js to /js/xenforo/bb_code_edit_original.js
2) Copy /js/xenforo/full/bb_code_edit.js to /js/xenforo/bb_code_edit.js
3) Edit /js/xenforo/bb_code_edit.js and comment out the following starting on line #57