tests/drivers/clock_control: stm32: Factorize wl/wb clear clocks overlay

Since they don't have impact on sysclock src configuration,
remove LSI/E clocks from clear clocks overlays.
This enables the possibility to factorize wl and wb clear clocks overlays
and brings some use cases factorizations as well.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>