zephyr: remove unused label property from eSPI emulator
zephyr: remove unused label property from eSPI emulator

The label property has been removed from the upstream Zephyr eSPI
emulator.

BUG=b:239165779
BRANCH=none
TEST=./twister --clobber

Signed-off-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Change-Id: Ief1eead62d2ccf20a27f1fd276ff64fe66136511
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3855430
Reviewed-by: Yuval Peress <50dc11c009bd4d7e9d9d15a383c1743ce5ee82ef@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec