MAINTAINERS: stmmac: retire Giuseppe Cavallaro

I tried to get stmmac maintainers to be more active by agreeing with
them off-list on a review rotation. I pinged Peppe 3 times over 2 weeks
during his "shift month", no reviews are flowing.

All the contributions are much appreciated! But stmmac is quite
active, we need participating maintainers :(

Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230726151120.1649474-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: kuba-moo

MAINTAINERS

@@ -20403,7 +20403,6 @@ F:	drivers/pwm/pwm-stm32*
 F:	include/linux/*/stm32-*tim*
 
 STMMAC ETHERNET DRIVER
-M:	Giuseppe Cavallaro <peppe.cavallaro@st.com>
 M:	Alexandre Torgue <alexandre.torgue@foss.st.com>
 M:	Jose Abreu <joabreu@synopsys.com>
 L:	netdev@vger.kernel.org