MAINTAINERS: remove DENG Qingfang from MediaTek switch

MAINTAINERS: remove DENG Qingfang from MediaTek switch

We have not seen tags from DENG Qingfang for the MediaTek
switch driver in over 5 years. He is active upstream with
PPP/PPPoE patches in net-next. Chester and Daniel are active.

Subsystem MEDIATEK SWITCH DRIVER
  Changes 26 / 70 (37%)
  Last activity: 2025-12-01
  Chester A. Unal <chester.a.unal@arinc9.com>:
    Tags 585943b7ad30 2025-12-01 00:00:00 7
  Daniel Golle <daniel@makrotopia.org>:
    Author 497041d76301 2025-04-23 00:00:00 2
    Tags 3b87e60d2131 2025-12-01 00:00:00 14
  DENG Qingfang <dqfext@gmail.com>:
  Sean Wang <sean.wang@mediatek.com>:
  Top reviewers:
    [4]: andrew@lunn.ch
    [4]: florian.fainelli@broadcom.com
    [4]: arinc.unal@arinc9.com
    [2]: olteanv@gmail.com
  INACTIVE MAINTAINER DENG Qingfang <dqfext@gmail.com>

Acked-by: Chester A. Unal <chester.a.unal@arinc9.com>
Link: https://patch.msgid.link/20260303215339.2333548-7-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>