OvmfPkg: Remove PcdPeiCoreMaxXXX PCDs' statement

OvmfPkg: Remove PcdPeiCoreMaxXXX PCDs' statement

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1405

The codes have been updated to not use PcdPeiCoreMaxFvSupported,
PcdPeiCoreMaxPeimPerFv and PcdPeiCoreMaxPpiSupported, so their
statement in platform DSC could be removed.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Julien Grall <julien.grall@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>