[bootlin/training-materials] 36dfe4: yocto: lab1: BBB: fix section title

[Luca Ceresoli]

  Branch: refs/heads/master
  Home:   https://github.com/bootlin/training-materials
  Commit: 36dfe480b3349b404e5b1ddf050b4e250a401485
      https://github.com/bootlin/training-materials/commit/36dfe480b3349b404e5b1ddf050b4e250a401485
  Author: Luca Ceresoli <luca.ceresoli at bootlin.com>
  Date:   2022-07-22 (Fri, 22 Jul 2022)

  Changed paths:
    M labs/yocto-first-build/yocto-first-build.tex

  Log Message:
  -----------
  yocto: lab1: BBB: fix section title

We do not configure the U-Boot environment, thus remove it from the section
title.

Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>