MAINTAINERS: Remove stale entry for BCM33xx chips

Commit 70371cef ("MAINTAINERS: Add entry for BMIPS multiplatform
kernel") supersedes this entry for BCM33xx.

Fixes: 70371cef

 ("MAINTAINERS: Add entry for BMIPS multiplatform kernel")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: blogic@openwrt.org
Cc: cernekee@gmail.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12301/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>