This commit removes all references to the `xtools` toolchain variant in the
board YAML files.
Note that the `xtools` toolchain variant has been deprecated since Zephyr
v3.3.0 and now removed.
The removal process was automated using the following command line:
git grep -l xtools -- boards/*.{yml,yaml} | \
xargs -n 1 -P $(nproc) \
yq -i 'del(.toolchain[] | select(. == "xtools"))'
Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
