We originally removed GUI-related layers from headless platforms in commit
ef26e935d0, but we left meta-webkit in the ccimx91's bblayers due to a
spurious selinux dependency. Since we recently removed both the webkit and
selinux layers from the ccimx95's bblayers in commit 2aaa76c963, do the same
for the ccimx91.
Signed-off-by: Gabriel Valcazar <gabriel.valcazar@digi.com>