dt-bindings: net: Drop unneeded quotes

Cleanup bindings dropping unneeded quotes. Once all these are fixed,
checking for this can be enabled in yamllint.

Acked-by: Marc Kleine-Budde <mkl@pengutronix.de> # for bindings/net/can
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp> # for bindings/net/toshiba,visconti-dwmac.yaml
Reviewed-by: Heiko Stuebner <heiko@sntech.de> #rockchip
Link: https://lore.kernel.org/r/20230320233758.2918972-1-robh@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>