Maintainers.txt: Remove MptScsi and PvScsi reviewers

Maintainers.txt: Remove MptScsi and PvScsi reviewers

The email addresses for the reviewers of the MptScsi and
PvScsi in the OvmfPkg are no longer valid.  Remove the
reviewers for the MptScsi and PvScsi drivers until new
maintainers/reviewers can be identified.

Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <quic_llindhol@quicinc.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>