ARM: dts: vf610-zii-dev-rev-b: Remove leftover PWM pingroup

Remove pwm0grp since it is:

	a) Not referenced anywhere in the DTS file (unlike Tower board it
	is based on, this board does not use/expose FTM0)

	b) Configures PTB2 and PTB3 in a way that contradicts
	pinctrl-mdio-mux

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Stefan Agner <stefan@agner.ch>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: andrew@lunn.ch
Cc: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Cc: cphealy@gmail.com
Tested-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>