Maintainers.txt: Update maintainer of MdeModulePkg

Maintainers.txt: Update maintainer of MdeModulePkg

Add Jian J Wang <jian.j.wang@intel.com> and
remove Eric Dong <eric.dong@intel.com>.
Eric is focusing on UefiCpuPkg.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>