west: boards: Remove accidental comma to fix pylint warning
west: boards: Remove accidental comma to fix pylint warning

Remove a trailing comma that generated a single-element tuple and made
pylint warn:

    scripts/west_commands/boards.py:50:8: W0106: Expression
    "(parser.add_argument(...), )" is assigned to nothing
    (expression-not-assigned)

No functional change.

Fixing pylint warnings for a CI check.

Signed-off-by: Ulf Magnusson <01743f1c1deb1fe75271d62edb65757d98ac0bcb@nordicsemi.no>

galak/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,nashif/zephyr,galak/zephyr