thermal/drivers/mediatek/lvts: Remove unused lvts_debugfs_exit

thermal/drivers/mediatek/lvts: Remove unused lvts_debugfs_exit

When debugfs is disabled, the function has no reference any more:

drivers/thermal/mediatek/lvts_thermal.c:266:13: error: 'lvts_debugfs_exit' defined but not used [-Werror=unused-function]
  266 | static void lvts_debugfs_exit(struct lvts_domain *lvts_td) { }
      |             ^~~~~~~~~~~~~~~~~

Fixes: ef280c17a840 ("thermal/drivers/mediatek/lvts: Fix debugfs unregister on failure")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20250505052502.1812867-1-arnd@kernel.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>